Electrical current generation system

ABSTRACT

An electrical generating system consists of a fuel cell, and an oxygen gas delivery. The fuel cell includes and anode channel having an anode gas inlet for receiving a supply of hydrogen gas, a cathode channel having a cathode gas inlet and a cathode gas outlet, and an electrolyte in communication with the anode and cathode channel for facilitating ion exchange between the anode and cathode channel. The oxygen gas delivery system is coupled to the cathode gas inlet and delivers oxygen gas to the cathode channel. The electrical current generating system also includes gas recirculation means couple to the cathode gas outlet for recirculating a portion of cathode exhaust gas exhausted from the cathode gas outlet to the cathode gas inlet.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation-in-part of priorinternational application No. PCT/CA99/00823, filed Sep. 14, 1999, whichclaimed priority from U.S. provisional application No. 60/100,091, filedSep. 14, 1998, and Canadian patent application No. 2,274,240, filed Jun.10, 1999, which applications are incorporated herein by reference.

FIELD

[0002] The present invention relates to a fuel cell for the generationof electrical current. In particular, the present invention relates to afuel cell-based electrical generation system which employs pressureswing adsorption for enhancing the efficiency of the fuel cell.

BACKGROUND

[0003] Fuel cells provide an environmentally friendly source ofelectrical current. One form of fuel cell used for generating electricalpower includes an anode for receiving hydrogen gas, a cathode forreceiving oxygen gas, and an alkaline electrolyte. Another form of fuelcell includes an anode channel for receiving a flow of hydrogen gas, acathode channel for receiving a flow of oxygen gas, and a polymerelectrolyte membrane (PEM) which separates the anode channel from thecathode channel. In both instances, oxygen gas which enters the cathodereacts with hydrogen ions which cross the electrolyte to generate a flowof electrons. Environmentally safe water vapor is also produced as abyproduct. However, several factors have limited the widespread use offuel cells as power generation systems.

[0004] In order to extract a continuous source of electrical power froma fuel cell, it is necessary to provide the fuel cell with a continuoussource of oxygen and hydrogen gas. However, with atmospheric air as thedirect source of oxygen to the cathode channel, performance of PEM fuelcells is severely impaired by the low partial pressure of oxygen and theconcentration polarization of nitrogen, while alkaline fuel cellsrequire a pretreatment purification system to remove carbon dioxide fromthe feed air. Further, as the average oxygen concentration in a cathodechannel with atmospheric air feed is typically only about 15%, the sizeof the fuel cell must be undesirably large in order to providesufficient power for industrial applications.

[0005] In order to achieve a partial pressure of oxygen through thecathode channel sufficient for the attainment of competitive currentdensities from a PEM fuel cell system, particularly for vehicularpropulsion, it is necessary to compress the air feed to at least 3atmospheres before the air feed is introduced to the cathode channel. Aswill be appreciated, the power input necessary to sufficiently compressthe air feed reduces the overall efficiency of the fuel cell system. Ithas been proposed to use polymeric membranes to enrich the oxygen, butsuch membranes actually reduce the oxygen partial pressure and thereduction in total pressure more than offsets the limited enrichmentattainable.

[0006] External production, purification, dispensing and storage ofhydrogen (either as compressed gas or cryogenic liquid) requires costlyinfrastructure, while storage of hydrogen fuel on vehicles presentsconsiderable technical and economic barriers. Accordingly, forstationary power generation, it is preferred to generate hydrogen fromnatural gas by steam reforming or partial oxidation followed by watergas shift. For fuel cell vehicles using a liquid fuel, it is preferredto generate hydrogen from methanol by steam reforming or from gasolineby partial oxidation of autothermal reforming, again followed by watergas shift. However, the resulting hydrogen contains carbon monoxide andcarbon dioxide impurities which cannot be tolerated respectively by thePEM fuel cell catalytic electrodes and the alkaline fuel cellelectrolyte in more than trace levels.

[0007] In prior art PEM fuel cells operating with an autothermal orpartial oxidation fuel processor, ambient air is used as the oxidant.This results in a large load of nitrogen having to be heated and thencooled through the fuel processor system. The substantial volume ofnitrogen contributes to pressure losses throughout the fuel processorand anode channels, or alternatively to the cost and physical bulkpenalties of making those passages larger.

[0008] While water recovery from fuel cell exhaust is highly desirablefor efficient fuel processor operation, the conventional fuel celldischarges its oxygen-depleted cathode exhaust gas to atmosphere, andthus requires an extra condenser to recover water which then must bevaporized in the fuel processor at a substantial energy cost. Thiscondenser adds to the radiator cooling load which is already a problemfor automotive fuel cell power plants in view of the large amount of lowgrade heat which must be rejected.

[0009] The conventional method of removing residual carbon monoxide fromthe hydrogen feed to PEM fuel cells has been catalytic selectiveoxidation, which compromises efficiency as both the carbon monoxide anda fraction of the hydrogen are consumed by low temperature oxidation,without any recovery of the heat of combustion. Palladium diffusionmembranes can be used for hydrogen purification, but have thedisadvantages of delivery of the purified hydrogen at low pressure, andalso the use of rare and costly materials.

[0010] Pressure swing adsorption systems (PSA) have the attractivefeatures of being able to provide continuous sources of oxygen andhydrogen gas, without significant contaminant levels. PSA systems andvacuum pressure swing adsorption systems (vacuum-PSA) separate gasfractions from a gas mixture by coordinating pressure cycling and flowreversals over an adsorbent bed which preferentially adsorbs a morereadily adsorbed gas component relative to a less readily adsorbed gascomponent of the mixture. The total pressure of the gas mixture in theadsorbent bed is elevated while the gas mixture is flowing through theadsorbent bed from a first end to a second end thereof, and is reducedwhile the gas mixture is flowing through the adsorbent from the secondend back to the first end. As the PSA cycle is repeated, the lessreadily adsorbed component is concentrated adjacent the second end ofthe adsorbent bed, while the more readily adsorbed component isconcentrated adjacent the first end of the adsorbent bed. As a result, a“light” product (a gas fraction depleted in the more readily adsorbedcomponent and enriched in the less readily adsorbed component) isdelivered from the second end of the bed, and a “heavy” product (a gasfraction enriched in the more strongly adsorbed component) is exhaustedfrom the first end of the bed.

[0011] However, the conventional system for implementing pressure swingadsorption or vacuum pressure swing adsorption uses two or morestationary adsorbent beds in parallel, with directional valving at eachend of each adsorbent bed to connect the beds in alternating sequence topressure sources and sinks. This system is often difficult and expensiveto implement due to the complexity of the valving required.

[0012] Further, the conventional PSA system makes inefficient use ofapplied energy, because feed gas pressurization is provided by acompressor whose delivery pressure is the highest pressure of the cycle.In PSA, energy expended in compressing the feed gas used forpressurization is then dissipated in throttling over valves over theinstantaneous pressure difference between the adsorber and the highpressure supply. Similarly, in vacuum-PSA, where the lower pressure ofthe cycle is established by a vacuum pump exhausting gas at thatpressure, energy is dissipated in throttling over valves duringcountercurrent blowdown of adsorbers whose pressure is being reduced. Afurther energy dissipation in both systems occurs in throttling of lightreflux gas used for purge, equalization, cocurrent blowdown and productpressurization or backfill steps. These energy sinks reduce the overallefficiency of the fuel cell system.

[0013] Additionally, conventional PSA systems can generally only operateat relatively low cycle frequencies, necessitating the use of largeadsorbent inventories. The consequent large size and weight of such PSAsystems renders them unsuitable for vehicular fuel cell applications.Thus, a conventional PSA unit for oxygen concentration would require anadsorbent bed volume of about 400 L, and an additional installed volumeof about 100 L for pressure enclosures and PSA cycle control valves, inorder to deliver a product flow containing about 200 L/min oxygen whichwould be sufficient for a 40 kW fuel cell.

[0014] Accordingly, there remains a need for an efficient fuelcell-based electrical generation system which can produce sufficientpower for industrial applications and which is suitable for vehicularapplications. There also remains a need for compact, lightweighthydrogen and oxygen PSA systems that operate at higher cycle frequenciesand are suitable for vehicular fuel cell-based applications.

SUMMARY OF THE INVENTION

[0015] According to the invention, there is provided a fuel cell-basedelectrical generation system which addresses the deficiencies of theprior art fuel cell electrical generation systems.

[0016] The electrical current generating system, according to a firstembodiment of the present invention, comprises a fuel cell, and anoxygen gas delivery system. The fuel cell includes an anode channelhaving an anode gas inlet for receiving a supply of hydrogen gas, acathode channel having a cathode gas inlet and a cathode gas outlet, andan electrolyte in communication with the anode and cathode channel forfacilitating ion exchange between the anode and cathode channel. Theoxygen gas delivery system is coupled to the cathode gas inlet anddelivers oxygen gas to the cathode channel.

[0017] The electrical current generating system also includes gasrecirculation means coupled to the cathode gas outlet for recirculatinga portion of cathode exhaust gas (which is still enriched in oxygenrelative to ambient air, and carries fuel cell exhaust water and fuelcell waste heat) from the cathode gas outlet to the cathode gas inlet.

[0018] In some embodiments, at least a portion of the cathode exhaustgas is returned to the inlet of an autothermal or partial oxidation fuelprocessor (or reformer) for reacting a hydrocarbon fuel with oxygen andsteam in order to generate raw hydrogen or syngas.

[0019] In a preferred implementation of the first embodiment, the oxygengas delivery system comprises an oxygen gas separation system forextracting enriched oxygen gas from air. Preferably, the oxygen gasseparating system comprises an oxygen pressure swing adsorption systemincluding a rotary module having a stator and a rotor rotatable relativeto the stator. The rotor includes a number of flow paths for receivingadsorbent material therein for preferentially adsorbing a first gascomponent in response to increasing pressure in the flow paths relativeto a second gas component. The pressure swing adsorption system alsoincludes compression machinery coupled to the rotary module forfacilitating gas flow through the flow paths for separating the firstgas component from the second gas component. The stator includes a firststator valve surface, a second stator valve surface, and plurality offunction compartments opening into the stator valve surfaces. Thefunction compartments include a gas fee compartment, a light reflux exitcompartment and a light reflux return compartment.

[0020] In one variation, the compression machinery comprises acompressor for delivering pressurized air to the gas feed compartment,and a light reflux expander coupled between the light reflux exitcompartment and the light reflux compartment. The gas recirculatingmeans comprises a compressor coupled to the light reflux expander forsupplying oxygen gas, exhausted from the cathode gas outlet, underpressure to the cathode gas inlet. As a result, energy recovered fromthe pressure swing adsorption system can be applied to boost thepressure of oxygen gas delivered to the cathode gas inlet.

[0021] In another variation, restrictor orifices are disposed betweenthe light reflux exit compartment and the light reflux returncompartment for pressure letdown in replacement of the light refluxexpander. The gas recirculating means comprises a compressor coupled tothe cathode gas outlet for supplying oxygen gas to the cathode gasinlet, and a restrictive orifice disposed between the cathode gas outletand a pressurization compartment for recycling a portion of the oxygengas as feed gas to the pressure swing adsorption system. As a result,energy recovered from the cathode gas outlet can be used to helppressurize the cathode gas inlet through the PSA system.

[0022] The electrical current generating system, according to a secondembodiment of the present invention, comprises a fuel cell, an oxygengas delivery system, and a hydrogen gas delivery system. The fuel cellincludes an anode channel having an anode gas inlet and an anode gasoutlet, a cathode channel having a cathode gas inlet and a cathode gasoutlet, and an electrolyte in communication with the anode and cathodechannel for facilitating ion exchange between the anode and cathodechannel.

[0023] The oxygen gas delivery system is coupled to the cathode gasinlet and delivers oxygen gas to the cathode channel. The hydrogen gasdelivery system includes a hydrogen gas inlet for receiving a firsthydrogen gas feed from the anode gas outlet, and a hydrogen gas outletcoupled to the anode gas inlet for delivering hydrogen gas received fromthe first hydrogen gas feed to the anode channel with increased purity.

[0024] In a preferred implementation of the second embodiment, theoxygen gas separation system comprises an oxygen pressure swingadsorption system, and the hydrogen gas separation system comprises areactor for producing a second hydrogen gas fee from hydrocarbon fuel,and a hydrogen pressure swing adsorption system coupled to the reactorfor purifying hydrogen gas received from the first and second hydrogengas feeds. Both pressure swing adsorption systems include a rotarymodule having a stator and a rotor rotatable relative to the stator. Therotor includes a number of flow paths for receiving adsorbent materialtherein for preferentially adsorbing a first gas component in responseto increasing pressure in the flow paths relative to a second gascomponent. The function compartments include a gas feed compartment anda heavy product compartment.

[0025] In one variation, the oxygen pressure swing adsorption systemincludes a compressor coupled to the gas feed compartment for deliveringpressurized air to the gas feed compartment, and a vacuum pump coupledto the compressor for extracting nitrogen product gas from the heavyproduct compartment. The reactor comprises a steam reformer, including aburner, for producing syngas, and a water gas shift reactor coupled tothe steam reformer for converting the syngas to the second hydrogen gasfeed. The hydrogen pressure swing adsorption system includes a vacuumpump for delivering fuel gas from the heavy product compartment to theburner. The fuel gas is burned in the burner, and the heat generatedtherefrom is used to supply the endothermic heat of reaction necessaryfor the steam reformer reaction. The resulting syngas is delivered tothe water gas shift reactor for removal of impurities, and thendelivered as the second hydrogen gas feed to the hydrogen pressure swingadsorption system.

[0026] In another variation, the invention includes a burner for burningfuel. The reactor comprises an autothermal reformer for producingsyngas, and a water gas shift reactor coupled to the autothermalreformer for converting the syngas to the second hydrogen gas fee. Thecompressor of the oxygen pressure swing adsorption system deliverspressurized air to the burner, and the heavy product gas is deliveredfrom the hydrogen pressure swing adsorption system as tail gas to beburned in the burner. The compression machine of the oxygen pressureswing adsorption system also includes an expander coupled to thecompressor for driving the compressor from hot gas of combustion emittedfrom the burner. Heat from the burner may also be used to preheat airand/or fuel supplied to the autothermal reformer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The preferred embodiment of the present invention will now bedescribed, by way of example only, with reference to the drawings, inwhich:

[0028]FIG. 1 is a sectional view of a rotary PSA module suitable for usewith the present invention, showing the stator and rotor situated in thestator.

[0029]FIG. 2 is a sectional view of the module of FIG. 1, with thestator deleted for clarity.

[0030]FIG. 3 is a sectional view of the stator shown in FIG. 1, with therotor deleted for clarity.

[0031]FIG. 4 is an axial section of the module of FIG. 1.

[0032]FIG. 5 shows a typical PSA cycle attainable with the PSA systemshown in FIGS. 1 to 4.

[0033]FIG. 6 shows one variation of the PSA cycle with heavy reflux,attainable with the PSA system shown in FIGS. 1 to 4.

[0034]FIG. 7 shows a pressure swing adsorption apparatus for separatingoxygen gas from air, suitable for use with the present invention, anddepicting the rotary module shown in FIG. 1 and a compression machinecoupled to the rotary module.

[0035]FIG. 8 shows a pressure swing adsorption apparatus for purifyinghydrogen gas, suitable for use with the present invention, and depictingthe rotary module shown in FIG. 1 and a compression machine coupled tothe rotary module.

[0036]FIG. 9 shows an electrical current generating system, according toa first embodiment of the present invention, including anoxygen-separating PSA system for supplying enriched oxygen to the fuelcell cathode channel with energy recovery from light reflux expansion toboost the pressure of oxygen circulating in the fuel cell cathode loop.

[0037]FIG. 10 shows a first variation of the electrical currentgenerating system shown in FIG. 9, but with the PSA system including acountercurrent blowdown expander driving a free rotor exhaust vacuumpump for vacuum-PSA operation.

[0038]FIG. 11 shows a second variation of the electrical currentgenerating system shown in FIG. 9, with a portion of the oxygen enrichedgas discharged from the fuel cell cathode being used for apressurization step for the PSA system.

[0039]FIG. 12 shows an electrical current generating system, accordingto a second embodiment of the present invention, including anoxygen-separating PSA system for supplying enriched oxygen to the fuelcell cathode channel, and a hydrogen-separating PSA system for supplyingenriched hydrogen to the fuel cell anode channel, with thehydrogen-separating PSA system receiving feed gas from a streamreformer.

[0040]FIG. 13 shows an electrical current generating system, accordingto a variation of the electrical current generating system shown in FIG.12, but with the hydrogen-separating PSA system receiving feed gas froman autothermal reformer.

[0041]FIG. 14 shows an electrical current generating system with carbondioxide removal and oxygen enrichment for an alkaline fuel cell, andwith an oxygen accumulator.

[0042]FIG. 15 shows an axial section of a rotary PSA module withrotating adsorbers and stationary distributor valves.

[0043]FIG. 16 shows a transverse section of the module of FIG. 15.

[0044]FIG. 17 shows a transverse section of the module of FIG. 15.

[0045]FIG. 18 shows a transverse section of the module of FIG. 15.

[0046]FIG. 19 shows a transverse section of the module of FIG. 15.

[0047]FIG. 20 shows a transverse section of the module of FIG. 15.

[0048]FIG. 21 shows a transverse section of the module of FIG. 15.

[0049]FIG. 22 shows an axial section of a rotary PSA module withstationary adsorbers and rotating distributor valves.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] To aid in understanding the present invention, a pressure swingadsorption process and associated apparatus, suitable for use with thepresent invention, will be described first, with reference to FIGS. 1through 6. Thereafter, an oxygen-separating pressure swing adsorptionsystem and a hydrogen-separating pressure swing adsorption system willbe described with reference to FIGS. 7 and 8 respectively. Twoembodiments of the invention, together with variations thereon, willthen be described commencing with FIG. 9.

[0051]FIGS. 1, 2, 3 and 4

[0052] A rotary module 10 which is suitable for use as part of thepresent invention is shown in FIGS. 1, 2, 3 and 4. The module includes arotor 11 revolving about axis 12 in the direction shown by arrow 13within stator 14. However, it should be understood that the invention isnot limited to PSA systems having rotary modules. Rather otherarrangements may be employed without departing from the scope of theinvention. For instance, if desired, the present invention may beemployed with multiple stationary adsorbent beds in parallel, withdirectional valving at each of each adsorbent bed to connect the beds inalternating sequence to pressure sources and sinks. However, as willbecome apparent, the rotary module 10 is preferred since it provideshighly desirable features of efficiency and compactness.

[0053] Rotary PSA modules include those with rotating adsorber modulesto provide the rotary valve function, and those with a fixed adsorbermodule cooperating with rotating valves, preferably coaxial to theadsorber module. In a particular embodiment, the rotary PSA module is acylindrical axial flow adsorber module, with feed and product rotaryvalve faces at opposite ends of the adsorber module. The adsorber modulemay rotate or remain stationary, the later version including fluidtransfer between the casing and the rotating valve rotors.

[0054] In general, the rotary module 10 may be configured for flowthrough the adsorber elements in the radial, axial or oblique conicaldirections relative to the rotor axis. For operation at high cyclefrequency, radial flow has the advantage that the centripetalacceleration will lie parallel to the flow path for most favorablestabilization of buoyancy-driven free convection. Radial flowconfigurations may be preferred for large module capacities.

[0055] Axial flow configurations may be preferred for smaller modulecapacities, and advantageously allow increased compactness of fuel cellsystems that incorporate PSA systems, at least for smaller power ratingsbelow about 300 kW. Compactness is an important consideration forenabling practicable use of PSA systems in automotive fuel cell powerplants.

[0056] As shown in FIG. 2, the rotor 11 is of annular section, havingconcentrically to axis 12 an outer cylindrical wall 20 whose externalsurface is first valve surface 21, and an inner cylindrical wall 22whose internal surface is second valve surface 23. The rotor has (in theplane of the section defined by arrows 15 and 16 in FIG. 4) a total of“N” radial flow adsorber elements 24. An adjacent pair of adsorberelements 25 and 26 are separated by partition 27 which is structurallyand sealingly joined to outer wall 20 and inner wall 22. Adjacentadsorber elements 25 and 26 are angularly spaced relative to axis 12 byan angle of 360°/N. Since the adsorber elements and the valve surfacesare thereby integrated into a single unit, and the adsorber elements arelocated in close proximity to the valve surfaces with minimal deadvolume, the rotary module 10 is more compact and efficient thanconventional PSA systems.

[0057] Adsorber element 24 has a first end 30 defined by support screen31 and a second end 32 defined by support screen 33. The adsorber may beprovided as granular adsorbent, whose packing voidage defines a flowpath contacting the adsorbent between the first and second ends of theadsorber. However, as described in copending U.S. patent applicationSer. No. 08/995,906, the description therein being incorporated hereinby reference, preferably the adsorber element is provided as an array oflaminated thin sheets extending between the first and second ends of theadsorber, the sheets having an adsorbent such as a zeolite supported ona reinforcement matrix, and with flow channels established by spacersbetween the sheets. The laminated sheet adsorber, with sheet thicknessof approximately 150 microns and using type X zeolites, has greatlyreduced mass transfer and pressure drop resistances compared toconventional granular adsorbers, so that satisfactory oxygen enrichmentoperation has been achieved with PSA cycle periods in the order of 1second and as low as 0.4 second. Consequently, the adsorbent inventoryis radically reduced compared to conventional PSA cycle periods of about1 minute, with the size of the module being smaller by some two ordersof magnitude compared to conventional PSA equipment of equivalentcapacity. As a result, an exceptionally compact PSA module that can beused, rendering the invention particularly suitable for vehicular fuelcell power plants.

[0058] First aperture or orifice 34 provides flow communication fromfirst valve surface 21 through wall 20 to the first end 30 of adsorber24. Second aperture or orifice 35 provides flow communication fromsecond valve surface 23 through wall 22 to the second end 31 of adsorber24. Support screens 31 and 33 respectively provide flow distribution 32between first aperture 34 and first end 30, and between second aperture35 and second end 32, of adsorber element 24.

[0059] As shown in FIG. 3, stator 14 is a pressure housing including anouter cylindrical shell or first valve stator 40 outside the annularrotor 11, and an inner cylindrical shell or second valve stator 41inside the annular rotor 11. Outer shell 40 carries axially extendingstrip seals (e.g. 42 and 43) sealingly engaged with first valve surface21, while inner shell 41 carries axially extending strip seals (e.g. 44and 45) sealingly engaged with second valve surface 23. Preferably, theazimuthal sealing width of the strip seals is greater than the diametersor azimuthal widths of the first and second apertures 34 and 35 openingthrough the first and second valve surfaces.

[0060] A set of first compartments in the outer shell each open in anannular sector to the first valve surface, and each provide fluidcommunication between its angular sector of the first valve surface anda manifold external to the module. The angular sectors of thecompartments are much wider than the angular separation of the adsorberelements. The first compartments are separated on the first sealingsurface by the strip seals (e.g. 42). Proceeding clockwise in FIG. 3, inthe direction of rotor rotation, a first feed pressurization compartment46 communicates by conduit 47 to first feed pressurization manifold 48,which is maintained at a first intermediate feed pressure. Similarly, asecond feed pressurization compartment 50 communicates to second feedpressurization manifold 51, which is maintained at a second intermediatefeed pressure higher than the first intermediate feed pressure but lessthan the higher working pressure.

[0061] For greater generality, module 10 is shown with provision forsequential admission of two feed mixtures, the first feed gas having alower concentration of the more readily adsorbed component relative tothe second feed gas. First feed compartment 52 communicates to firstfeed manifold 53, which is maintained at substantially the higherworking pressure. Likewise, second feed compartment 54 communicates tosecond feed manifold 55, which is maintained at substantially the higherworking pressure. A first countercurrent blowdown compartment 56communicates to first countercurrent blowdown manifold 57, which ismaintained at a first countercurrent blowdown intermediate pressure. Asecond countercurrent blowdown compartment 58 communicates to secondcountercurrent blowdown manifold 59, which is maintained at a secondcountercurrent blowdown intermediate pressure above the lower workingpressure. A heavy product compartment 60 communicates to heavy productexhaust manifold 61 which is maintained at substantially the lowerworking pressure. It will be noted that compartment 58 is bounded bystrip seals 42 and 43, and similarly all the compartments are boundedand mutually isolated by strip seals.

[0062] A set of second compartments in the inner shell each open in anangular sector to the second valve surface, and each provide fluidcommunication between its angular sector of the second valve surface anda manifold external to the module. The second compartments are separatedon the second sealing surface by the strip seals (e.g. 44). Proceedingclockwise in FIG. 3, again in the direction of rotor rotation, lightproduct compartment 70 communicates to light product manifold 71, andreceives high product gas at substantially the higher working pressure,less frictional pressure drops through the adsorbers and the first andsecond orifices. According to the angular extension of compartment 70relative to compartment 52 and 54, the light product may be obtainedonly from adsorbers simultaneously receiving the first feed gas fromcompartment 52, or from adsorbers receiving both the first and secondfeed gases.

[0063] A first light reflux exit compartment 72 communicates to firstlight reflux exit manifold 73, which is maintained at a first lightreflux exit pressure, here substantially the higher working pressureless frictional pressure drops. A first cocurrent blowndown compartment74 (which is actually the second light reflux exit compartment),communicates to second light reflux exit manifold 75, which ismaintained at a first cocurrent blowdown pressure less than the higherworking pressure. A second cocurrent blowdown compartment or third lightreflux exit compartment 76 communicates to third light reflux exitmanifold 77, which is maintained at a second cocurrent blowdown pressureless than the first cocurrent blowdown pressure. A third cocurrentblowdown compartment or fourth light reflux exit compartment 78communicates to fourth light reflux exit manifold 79, which ismaintained at a third cocurrent blowdown pressure less than the secondcocurrent blowdown pressure.

[0064] A purge compartment 80 communicates to a fourth light refluxreturn manifold 81, which supplies the fourth light reflux gas which hasbeen expanded form the third cocurrent blowdown pressure tosubstantially the lower working pressure with an allowance forfrictional pressure drops. The ordering of light reflux pressurizationsteps is inverted from the ordering or light reflux exit or cocurrentblowdown steps, so as to maintain a desirable “last out—first in”stratification of light reflux gas packets. Hence a first light refluxpressurization compartment 82 communicates to a third light refluxreturn manifold 83, which supplies the third light reflux gas which hasbeen expanded from the second cocurrent blowdown pressure to a firstlight reflux pressurization pressure greater than the lower workingpressure. A second light reflux pressurization compartment 84communicates to a second light reflux return manifold 85, which suppliesthe second light reflux gas which has been expanded from the firstcocurrent blowdown pressure to a second light reflux pressurizationpressure greater than the first light reflux pressurization pressure.Finally, a third light reflux pressurization compartment 86 communicatesto a first light reflux return manifold 87, which supplies the firstlight reflux gas which has been expanded from approximately the higherpressure to a third light reflux pressurization pressure greater thanthe second light reflux pressurization pressure, and in this exampleless than the first feed pressurization pressure.

[0065] Additional details are shown in FIG. 4. Conduits 88 connect firstcompartment 60 to manifold 61, with multiple conduits providing for goodaxial flow distribution in compartment 60. Similarly, conduits 89connect second compartment 80 to manifold 81. Stator 14 has base 90 withbearings 91 and 92. Motor 95 is coupled to shaft 94 to drive rotor 11.The rotor could alternatively rotate as an annular drum, supported byrollers at several angular positions about its rim and also driven atits rim so that no shaft would be required. A rim drive could beprovided by a ring gear attached to the rotor, or by a linearelectromagnetic motor whose stator would engage an arc of the rim.Particularly for hydrogen separation applications, the rotor drive maybe hermetically enclosed within the stator housing to eliminate hazardsrelated to seal leakage. Outer circumferential seals 96 seal the ends ofouter strip seals 42 and the edges of first valve surface 21, whileinner circumferential seals 97 seal the ends of inner strip seals 44 andthe edges of second valve surface 23. Rotor 11 has access plug 98between outer wall 20 and inner wall 22, which provides access forinstallation and removal of the adsorbent in adsorbers 24.

[0066]FIGS. 5 and 6

[0067]FIG. 5 shows a typical PSA cycle which would be obtained using theforegoing gas separation system, while FIG. 6 shows a similar PSA cyclewith heavy reflux recompression of a portion of the first product gas toprovide a second feed gas to the process.

[0068] In FIGS. 5 and 6, the vertical axis 150 indicates the workingpressure in the adsorbers and the pressure in the first and secondcompartments. Pressure drops due to flow within the adsorber elementsare neglected. The higher and lower working pressures are respectivelyindicated by dotted lines 151 and 152. The lower working pressure may benominally or approximately ambient atmospheric pressure, or may be asubatmospheric pressure established by vacuum pumping. The higherworking pressure may typically be in the range of twice to four timesthe lower working pressure, based on the ratio of absolute pressures.

[0069] The horizontal axis 155 of FIGS. 5 and 6 indicates time, with thePSA cycle period defined by the time interval between points 156 and157. At times 156 and 157, the working pressure in a particular adsorberis pressure 158. Starting from time 156, the cycle for a particularadsorber (e.g. 24) begins as the first aperture 34 of that adsorber isopened to the first feed pressurization compartment 46, which is fed byfirst feed supply means 160 at the first intermediate feed pressure 161.The pressure in that adsorber rises from pressure 158 at time 157 to thefirst intermediate feed pressure 161. Proceeding ahead, first aperturepasses over a seal strip, first closing adsorber 24 to compartment 46and then opening it to second feed pressurization compartment 50 whichis feed by second feed supply means 162 at the second intermediate feedpressure 163. The adsorber pressure rises to the second intermediatefeed pressure.

[0070] First aperture 34 of adsorber 24 is opened next to first feedcompartment 52, which is maintained at substantially the higher pressureby a third feed supply means 165. Once the adsorber pressure has risento substantially the higher working pressure, its second aperture 35(which has been closed to all second compartments since time 156) opensto light product compartment 70 and delivers light product 166.

[0071] In the cycle of FIG. 6, first aperture 34 of adsorber 24 isopened next to second feed compartment 54, also maintained atsubstantially the higher pressure by a fourth feed supply means 167. Ingeneral, the fourth feed supply means supplies a second feed gas,typically richer in the more readily adsorbed component than the firstfeed gas provided by the first, second and third feed supply means. Inthe specific cycle illustrated in FIG. 6, the fourth feed supply means167 is a “heavy reflux” compressor, recompressing a portion of the heavyproduct back into the apparatus. In the cycle illustrated in FIG. 5,there is no fourth feed supply means, and compartment 54 could beeliminated or consolidated with compartment 52 extended over a widerangular arc to the stator.

[0072] While feed gas is still being supplied to the first end ofadsorber 24 from either compartment 52 or 54, the second end of adsorber24 is closed to light product compartment 70 and opens to first refluxexit compartment 72 while delivering “light reflux” gas (enriched in theless readily adsorbed component, similar to second product gas) to firstlight reflux pressure let-down means (or expander) 170. The firstaperture 34 of adsorber 24 is then closed to all first compartments,while the second aperture 35 is opened successively to (a) second lightreflux exit compartment 74, dropping the adsorber pressure to the firstcocurrent blowdown pressure 171 while delivering light reflux gas tosecond light reflux pressure letdown means 172, (b) third light refluxexit compartment 76, dropping the adsorber pressure to the secondcocurrent blowdown pressure 173 while delivering light reflux gas tothird light reflux pressure letdown means 174, and (c) fourth lightreflux exit compartment 78, dropping the adsorber pressure to the thirdcocurrent blowdown pressure 175 while delivering light reflux gas tofourth light reflux pressure letdown means 176. Second aperture 35 isthen closed for an interval, until the light reflux return stepsfollowing the countercurrent blowdown steps.

[0073] The light reflux pressure let-down means may be mechanicalexpanders or expansion stages for expansion energy recovery, or may berestrictor orifices or throttle valves for irreversible pressurelet-down.

[0074] Either when the second aperture is closed after the final lightreflux exit step (as shown in FIGS. 5 and 6), or earlier while lightreflux exit steps are still underway, first aperture 34 is opened tofirst countercurrent blowdown compartment 56, dropping the adsorberpressure to the first countercurrent blowdown intermediate pressure 180while releasing “heavy” gas (enriched in the more strongly adsorbedcomponent) to first exhaust means 181. Then, first aperture 34 is openedto second countercurrent blowdown compartment 58, dropping the adsorberpressure to the first countercurrent blowndown intermediate pressure 182while releasing heavy gas to second exhaust means 183. Finally reachingthe lower working pressure, first aperture 34 is opened to heavy productcompartment 60, dropping the adsorber pressure to the lower pressure 152while releasing heavy gas to third exhaust means 184. Once the adsorberpressure has substantially reached the lower pressure while firstaperture 34 is open to compartment 60, the second aperture 35 opens topurge compartment 80, which receives fourth light reflux gas from fourthlight reflux pressure let-down means 176 in order to displace more heavygas into first product compartment 60.

[0075] In FIG. 5, the heavy gas from the first, second and third exhaustmeans is delivered as the heavy product 185. In FIG. 6, this gas ispartly released as the heavy product 185, while the balance isredirected as “heavy reflux” 187 to the heavy reflux compressor asfourth feed supply means 167. Just as light reflux enables an approachto high purity of the less readily adsorbed (“light”) component in thelight product, heavy reflux enables an approach to high purity of themore readily adsorbed (“heavy”) component in the heavy product so thathigh recovery of the less readily adsorbed (“light”) product can beachieved.

[0076] The adsorber is then repressurized by light reflux gas after thefirst and second apertures close to compartments 60 and 80. Insuccession, while the first aperture 34 remains closed at leastinitially, (a) the second aperture 35 is opened to first light refluxpressurization compartment 82 to raise the adsorber pressure to thefirst light reflux pressurization pressure 190 while receiving thirdlight reflux gas from the third reflux pressure letdown means 174, (b)the second aperture 35 is opened to second light reflux pressurizationcompartment 84 to raise the adsorber pressure to the second light refluxpressurization pressure 191 while receiving second light reflux gas fromthe second light reflux pressure letdown means 172, and (c) the secondaperture 35 is opened to third light reflux pressurization compartment86 to raise the adsorber pressure to the third light refluxpressurization pressure 192 while receiving first light reflux gas fromthe first light reflux pressure letdown means 170. Unless feedpressurization has already been started while light reflux return forlight reflux pressurization is still underway, the process (as based onFIGS. 5 and 6) begins feed pressurization for the cycle after time 157as soon as the third light reflux pressurization step has beenconcluded.

[0077] The pressure variation waveform in each adsorber would be arectangular staircase if there were no throttling in the first andsecond valves. Such throttling is needed to smooth pressure and flowtransients. In order to provide balanced performance, preferably all ofthe adsorber elements and the apertures are closely identical to eachother.

[0078] The rate of pressure change in each pressurization or blowdownstep will be restricted by throttling in ports (or in clearance orlabyrinth sealing gaps) of the first and second valve means, or bythrottling in the apertures at first and second ends of the adsorbers,resulting in the typical pressure waveform depicted in FIGS. 5 and 6.Alternatively, the apertures may be opened slowly by the seal strips, toprovide flow restriction throttling between the apertures and the sealstrips, which may have narrow tapered clearance channels so that theapertures are only opened to full flow gradually. Excessively rapidrates of pressure change would subject the adsorber to mechanicalstress, while also causing flow transients which would tend to increaseaxial dispersion of the concentration wavefront in the adsorber.Pulsations of flow and pressure are minimized by having a plurality ofadsorbers simultaneously transiting each step of the cycle, and byproviding enough volume in the function compartments and associatedmanifolds so that they act effectively as surge adsorbers between thecompression machinery and the first and second valve means.

[0079] It will be evident that the cycle could be generalized in manyvariations by having more or fewer intermediate stages in each majorstep of feed pressurization, countercurrent blowdown exhaust, or lightreflux. If desired, combined feed and product pressurization steps (orcombined cocurrent and countercurrent blowdown steps) at intermediatepressures may be performed from both first and second valvessimultaneously. The pressure at which feed pressurization begins, maydiffer from the pressure at which countercurrent blowdown begins.Furthermore, in air separation or air purification applications, a stageof feed pressurization (typically the first stage) could be performed byequalization with atmosphere as an intermediate pressure of the cycle.Similarly, a stage of countercurrent blowdown could be performed byequalization with atmosphere as an intermediate pressure of the cycle.

[0080]FIG. 7

[0081]FIG. 7 is a simplified schematic of a PSA system for separatingoxygen from air using nitrogen-selective zeolite adsorbents. The lightproduct is concentrated oxygen, while the heavy product isnitrogen-enriched air usually vented as waste. The cycle lower pressure152 is illustrated as nominally atmospheric pressure, although a vacuumpressure 152 could be used as will be illustrated in FIG. 8. Feed air isintroduced through filter intake 200 to a feed compressor 201. The feedcompressor includes compressor first stage 202, intercooler 203,compressor second stage 204, second intercooler 205, compressor thirdstage 206, third intercooler 207, and compressor fourth stage 208. Thefeed compressor 201 as described may be a four stage axial compressorwith motor 209 as prime mover coupled by shaft 210. The intercoolers areoptional. With reference to FIG. 5, the feed compressor first and secondstages are the first feed supply means 160, delivering feed gas at thefirst intermediate feed pressure 161 via conduit 212 and watercondensate separator 213 to first feed pressurization manifold 48. Feedcompressor third stage 206 is the second feed supply means 162,delivering feed gas at the second intermediate feed pressure 163 viaconduit 214 and water condensate separator 215 to second feedpressurization manifold 51. Feed compressor fourth stage 208 is thethird feed supply means 165, delivering feed gas at the higher pressure151 via conduit 216 and water condensate separator 217 to feed manifold53. Light product oxygen flow is delivered from light product manifold71 by conduit 218, maintained at substantially the higher pressure lessfrictional pressure drops.

[0082] The PSA system of FIG. 7 includes energy recovery expanders,including light reflux expander 220 (here including four stages) andcountercurrent blowdown expander 221 (here including two stages),coupled to feed compressor 201 by shaft 222. The expander stages may beprovided for example as radial inflow turbine stages, as full admissionaxial turbine stages with separate wheels, or as partial admissionimpulse turbine stages combined in a single wheel.

[0083] Light reflux gas from first light reflux exit manifold 73 flowsat the higher pressure via conduit 224 and heater 225 to first lightpressure letdown means 170 which here is first light reflux expanderstage 226, and then flows at the third light reflux pressurizationpressure 192 by conduit 227 to the first light reflux return manifold87. Light reflux gas from second light reflux exit manifold 75 flows atthe first cocurrent blowdown pressure 171 via conduit 228 and heater 225to second light reflux pressure letdown means 172, here the secondexpander stage 230, and then flows at the second light refluxpressurization pressure 191 by conduit 231 to the second light refluxreturn manifold 85. Light reflux gas from third light reflux exitmanifold 77 flows at the second cocurrent blowdown pressure 173 viaconduit 232 and heater 225 to third light reflux pressure pressurizationpressure 190 by conduit 235 to the third light reflux return manifold83. Finally, light reflux gas from fourth light reflux exit manifold 79flows at the third cocurrent blowdown pressure 175 via conduit 236 andheater 225 to fourth light reflux pressure letdown means 176, here thefourth light reflux expander stage 238, and then flows at substantiallythe lower pressure 152 by conduit 239 to the fourth light reflux returnmanifold 81.

[0084] Heavy countercurrent blowdown gas from first countercurrentblowdown manifold 57 flows at first countercurrent blowdown intermediatepressure 180 by conduit 240 to heater 241 and thence to first stage 242of the countercurrent blowdown expander 221 as first exhaust means 181,and is discharged from the expander to exhaust manifold 243 atsubstantially the lower pressure 152. Countercurrent blowdown gas fromsecond countercurrent blowdown manifold 59 flows at secondcountercurrent blowdown intermediate pressure 182 by conduit 244 toheater 241 and thence to second stage 245 of the countercurrent blowdownexpander 221 as second exhaust means 183, and is discharged from theexpander to exhaust manifold 243 at substantially the lower pressure152. Finally, heavy gas from heavy product exhaust manifold 61 flows byconduit 246 as third exhaust means 184 to exhaust manifold 243delivering the heavy product gas 185 to be vented at substantially thelower pressure 152.

[0085] Optional heaters 225 and 241 raise the temperatures of gasesentering expanders 220 and 221, thus augmenting the recovery ofexpansion energy and increasing the power transmitted by shaft 222 fromexpanders 220 and 221 to feed compressor 201, and reducing the powerrequired from prime mover 209. While heaters 225 and 241 are means toprovide heat to the expanders, intercoolers 203, 205 and 207 are meansto remove heat from the feed compressor and serve to reduce the requiredpower of the higher compressor stages. The intercoolers 203, 205, 207are optional features.

[0086] If light reflux heater 249 operates at a sufficiently hightemperature so that the exit temperature of the light reflux expansionstages is higher than the temperature at which feed gas is delivered tothe feed manifolds by conduits 212, 214 and 216, the temperature of thesecond ends 35 of the adsorbers 24 may be higher than the temperature oftheir first ends 34. Hence, the adsorbers have a thermal gradient alongthe flow path, with higher temperature at their second end relative tothe first end. This is an extension of the principle of :thermallycoupled pressure swing adsorption” (TCPSA), introduced by Keefer in U.S.Pat. No. 4,702,903. Adsorber rotor 11 then acts as a thermal rotaryregenerator, as in regenerative gas turbine engines having a compressor201 and an expander 220. Heat provided to the PSA process by heater 225assists powering the process according to a regenerative thermodynamicpower cycle, similar to advanced regenerative gas turbine enginesapproximately realizing the Ericsson thermodynamic cycle withintercooling on the compression side and interstage heating on theexpansion side. In the instance of PSA applied to oxygen separation fromair, the total light reflux flow is much less than the feed flow becauseof the strong bulk adsorption of nitrogen. Accordingly the powerrecoverable from the expanders is much less than the power required bythe compressor, but will still contribute significantly to enhancedefficiency of oxygen production.

[0087] If high energy efficiency is not of highest importance, the lightreflux expander stages and the countercurrent blowdown expander stagesmay be replaced by restrictor orifices or throttle valves for pressureletdown. The schematic of FIG. 7 shows a single shaft supporting thecompressor stages, the countercurrent blowdown or exhaust expanderstages, and the light reflux stages, as well as coupling the compressorto the prime mover. However, it should be understood that separateshafts and even separate prime movers may be used for the distinctcompression and expansion stages within the scope of the presentinvention.

[0088]FIG. 8

[0089]FIG. 8 shows a vacuum-PSA system, also with heavy product refluxas could be used to achieve high recovery in hydrogen purification forfuel cell power plant. The raw hydrogen may be provided in certainstationary applications from chemical process or petroleum refineryoffgases. However, in most fuel cell applications, the raw hydrogen gasfeed will be provided by processing of a hydrocarbon or carbonaceousfuel, e.g. by steam reforming of natural gas or methanol, or byautothermal reforming or partial oxidation of liquid fuels. Suchhydrogen feed gases typically contain 30% to 75% hydrogen. Using typicaladsorbents such as zeolites, carbon dioxide, carbon monoxide, nitrogen,ammonia, and hydrogen sulfide or other trace impurities will be muchmore readily adsorbed than hydrogen, so the purified hydrogen will bethe light product delivered at the higher working pressure which may beonly slightly less than the feed supply pressure, while the impuritieswill be concentrated as the heavy product and will be exhausted from thePSA process as “PSA tail gas” at the lower working pressure. This tailgas will be used as fuel gas for the fuel processing reactions togenerate hydrogen, or else for a combustion turbine to power PSAcompression machinery for the fuel cell power plant.

[0090] The PSA system of FIG. 8 has infeed conduit 300 to introduce thefeed gas at substantially the higher pressure to first feed manifold 53.In this example, all but the final pressurization steps are achievedwith light reflux gas, with the final feed pressurization step beingachieved through manifold 55.

[0091] The PSA system includes a multistage vacuum pump 301 driven byprime mover 209 through shaft 210, and optionally by light refluxexpander 220 through shaft 309. The vacuum pump 301 includes a firststage 302 drawing heavy gas by conduit 246 from first product exhaustmanifold 61, and compressing this gas through intercooler 303 to secondstage 304. Vacuum pump second stage 304 draws heavy gas from secondcountercurrent blowdown manifold 59 through conduit 244, and deliversthis gas by intercooler 305 to third stage 306 which also draws heavygas from first countercurrent blowdown manifold 57 through conduit 240.The vacuum pump stage 306 compresses the heavy gas to a pressuresufficiently above ambient pressure for a portion of this gas (heavyproduct gas or PSA tail gas) to be delivered for use as fuel has inheavy product delivery conduit 307. The remaining heavy gas proceedsfrom vacuum pump 301 to heavy reflux compressor 308 which attainssubstantially the higher working pressure of the PSA cycle.

[0092] The compressed heavy gas is conveyed from compressor fourth stage308 by conduit 310 to condensate separator 311. If desired (as forcombustion in an expansion turbine as in the embodiment of FIG. 13), theentire heavy product stream could be compressed through compressor 308,so that the heavy product fuel gas may be delivered at the highestworking pressure by alternative heavy product delivery conduit 312 whichis externally maintained at substantially the higher pressure lessfrictional pressure drops. Condensed vapors (such as water) are removedthrough conduit 313 at substantially the same pressure as the heavyproduct in conduit 312. The remaining heavy gas flow, after removal ofthe first product, gas, flows by conduit 314 to the second feed manifold55 as heavy reflux to the adsorbers following the feed step for eachadsorber. The heavy reflux gas is a second feed gas, of higherconcentration in the more readily adsorbed component or fraction thanthe first feed gas.

[0093]FIGS. 9 and 10

[0094] Turning now to FIGS. 9 and 10, fuel cell-based electrical currentgenerating systems, according to a first embodiment of the presentinvention, are shown using a rotary PSA system similar to that shown inFIG. 7 as the basic building block. However, it should be understoodthat the invention is not limited to electrical current generatingsystems having rotary PSA modules. Rather other arrangements may beemployed without departing from the scope of the invention.

[0095] In FIG. 9, the PSA system separates oxygen from air, usingnitrogen-selective zeolite adsorbents, as previously described. Thelight product is concentrated oxygen, while the heavy product isnitrogen-enriched air usually vented as waste. The cycle lower pressure152 is nominally atmospheric pressure, unless an optional vacuum pump isprovided as in FIG. 8. Feed air is introduced through filter intake 200to a feed compressor 201. The feed compressor includes compressor firststage 202, compressor second stage 204, compressor third stage 206, andcompressor fourth stage 208. The feed compressor 201 as described may bea four stage axial compressor with motor 209 as prime mover coupled byshaft 210. The compressor stages may be in series as shown, oralternatively in parallel. Intercoolers between compressor stages areoptional. The feed compressor first and second stages deliver feed gasat the first intermediate feed pressure 161 via conduit 212 and watercondensate separator 213 to first feed pressurization manifold 48. Feedcompressor third stage 206 delivers feed gas at the second intermediatefeed pressure 163 via conduit 214 and water condensate separator 215 tosecond feed pressurization manifold 51. Feed compressor fourth stage 208delivers feed gas at the higher pressure 151 via conduit 216 and watercondensate separator 217 to feed manifold 53. Light product oxygen flowis delivered from light product manifold 71 by conduit 218, maintainedat substantially the higher pressure less frictional pressure drops.

[0096] The apparatus of FIG. 9 includes energy recovery expanders,including light reflux expander 220 (here including four stages) andcountercurrent blowdown expander 221 (here including two stages).Expander 221 is coupled to feed compressor 201 by shaft 222. Theexpander stages may be provided for example as radial inflow turbinestages, as full admission axial turbine stages with separate wheels, oras partial admission turbine stages combined in a single wheel. If highenergy efficiency were not of highest importance, the light refluxexpander stages and/or the countercurrent blowdown expander stages couldbe replaced by restrictor orifices or throttle valves for pressureletdown.

[0097] Light reflux gas from light reflux exit manifold 73 flows at thehigher pressure via conduit 224 and heater 225 to first light refluxexpander stage 226, and then flows at the third light refluxpressurization pressure 192 by conduit 227 to the first light refluxreturn manifold 87. Light reflux gas from second light reflux exitmanifold 75 flows at the first cocurrent blowdown pressure 171 viaconduit 228 and heater 225 to the second expander stage 230, and thenflows at the second light reflux pressurization pressure 191 by conduit231 to the second light reflux return manifold 85. Light reflux gas fromthird light reflux exit manifold 77 flows at the second cocurrentblowdown pressure 173 via conduit 232 and heater 225 to the thirdexpander stage 234, and then flows at the first light refluxpressurization pressure 190 by conduit 235 to the third light refluxreturn manifold 83. Finally, light reflux gas from fourth light refluxexit manifold 79 flows at the third cocurrent blowdown pressure 175 viaconduit 236 and heater 225 to fourth light reflux expander stage 238,and then flows at substantially the lower pressure 152 by conduit 239 tothe fourth light reflux return manifold 81.

[0098] Heavy countercurrent blowdown gas from first countercurrentblowdown manifold 57 flows at first countercurrent blowdown intermediatepressure 180 by conduit 240 to heater 241 and thence to first stage 242of the countercurrent blowdown expander 221, and is discharged from theexpander to exhaust manifold 243 at substantially the lower pressure152.

[0099] Optional heaters 225 and 241 raise the temperature of gasesentering expanders 220 and 221, thus augmenting the recovery ofexpansion energy and increasing the power transmitted by shaft 222 fromexpanders 220 and 221 to feed compressor 201, and reducing the powerrequired from prime mover 209.

[0100] In the instance of PSA applied to oxygen separation from air, thetotal light reflux flow is much less than the feed flow because of thestrong bulk adsorption of nitrogen. Accordingly the power recoverablefrom the expanders is much less than the power required by thecompressor, but will still contribute significantly to enhancedefficiency of oxygen production. By operating the adsorbers atmoderately elevated temperature (e.g. 40° to 60° C.) and using stronglynitrogen-selective adsorbents such as Ca—X, Li—X or lithium chabazitezeolites, the PSA oxygen generation system can operate with favorableperformance and efficiency. Calcium or strontium exchanged chabazite maybe used at higher temperatures, even in excess of 100° C., reflectingthe extraordinary capacity of these adsorbents for nitrogen, theirnitrogen uptake being too close to saturation at lower temperatures nearambient for satisfactory operation.

[0101] While higher temperature of the adsorbent will reduce nitrogenuptake and selectivity for each zeolite adsorbent, the isotherms will bemore linear and humidity rejection will be easier. Working withadsorbents such as Ca—X and Li—X, recent conventional practice has beento operate ambient temperature PSA at subatmospheric lower pressures inso-called “vacuum swing adsorption” (VSA), so that the highly selectiveadsorbents operate well below saturation in nitrogen uptake, and have alarge working capacity in a relatively linear isotherm range. At highertemperatures, saturation in nitrogen uptake is shifted to more elevatedpressures, so that optimum PSA cycle higher and lower pressures are alsoshifted upward.

[0102] The enriched oxygen product gas is delivered by conduit 218,non-return valve 250, and conduit 251 to the inlet of oxygen productcompressor 252 which boosts the pressure of product oxygen delivered byconduit 253. Compressor 252 may be a single stage centrifugalcompressor, driven directly through shaft 254 by light reflux expander220 or alternatively by a motor. Light reflux expander 220 may be thesole power source to compressor 252, in which case expander 220 andcompressor 252 together constitute a free rotor turbo-booster 255. Sincethe working fluid in both expander 220 and compressor 252 is enrichedoxygen, the free rotor turbo-booster embodiment has the important safetyfeature of not requiring a shaft seal to an external motor. Preferably,energy recovered from light reflux expansion is used to raise thedelivery pressure of the light product, here oxygen.

[0103] The compressed enriched oxygen is delivered to a fuel cell 260,by conduit 253 to cathode inlet 261 of fuel cell cathode channel 262.Fuel cell 260 may be of the polymer electrolyte membrane (PEM), with theelectrolyte 265 separating cathode channel 262 from anode channel 266.Hydrogen fuel is supplied to anode inlet 267 of anode channel 266 byhydrogen infeed conduit 268.

[0104] The enriched oxygen passes through cathode channel 262 to cathodeexit 270, as a fraction of the oxygen reacts with hydrogen ions crossingthe membrane to generate electrical power and reacting to form byproductwater. The cathode exit gas leaving the cathode channel in conduit 280from cathode exit 270 (in this preferred embodiment) is stillsignificantly enriched in oxygen relative to ambient air concentrationof approximately 21%. A minor portion of this gas is purged as cathodepurge gas from conduit 280 by purge valve 285 and purge exhaust 286, andthe balance of the cathode exit gas is retained as cathode recycle gas.The cathode recycle gas is conveyed by conduit 281 to water condensateseparator 282 where excess liquid water is removed from the cathode exitgas, which remains saturated in water vapor. The humid cathode recyclegas is then blended with incoming enriched oxygen form the PSA system byconduit 283 connecting to conduit 251.

[0105] Conduits 251, 253, 280, 281 and 283 thus form a cathode loop withcathode channel 262, compressor 252 and water condensate separator 282.Heat exchanger 225 may cool the oxygen-enriched gas to be compressed bycompressor 252, by removing waste heat from the fuel cell cathode loopto heat light reflux gas before expansion in expander 220. Enough of thecathode exit gas is purged by purge valve 285 to avoid excessivebuild-up of argon and nitrogen impurities in the cathode loop. In apracticable example, the product oxygen concentration in conduit 218 maybe 90% oxygen, with equal amounts of argon and nitrogen impurities. Witha small purge flow, oxygen concentrations at cathode inlet 261 and atcathode exit 270 may be respectively 60% and 50%.

[0106] As discussed above, a PEM fuel cell operating with atmosphericair as oxidant may typically require air compression to at least 3atmospheres in order to achieve a sufficiently high oxygen partialpressure over the cathode for competitive current density in the fuelcell stack. Oxygen concentration at the cathode inlet would be 21%, andat the cathode exit typically only about 10% oxygen. The presentinvention can achieve much higher average oxygen concentration over thefuel cell cathode channel, e.g. 55% compared to approximately 15%.Hence, the operating pressure may be reduced to about 1.5 atmosphereswhile still retaining a substantial enhancement of oxygen partialpressure over the cathode. With higher oxygen partial pressure over thecathode, fuel cell stack power density and efficiency can be enhanced,as is particularly crucial in automotive power plant applications.Mechanical compression power required by the apparatus of the presentinvention (using high performance adsorbents such as Li—X) will be lessthan that required for the air compressor of a PEM fuel cell systemoperating at 3 atmospheres air supply pressure, further enhancingoverall power plant efficiency.

[0107] An important benefit in this example apparatus is that the oxygenenriched gas entering cathode inlet 261 is humidified by blending withthe much larger stream of saturated cathode recycle gas. Another benefitis that energy recovery from the PSA unit can be applied to boostpressure and drive recycle circulation in the cathode loop, while fuelcell waste heat can be applied to heat exchangers 225 and 241 to enhanceexpansion energy recovery in the PSA unit. Yet another benefit is thatsuitable cathode channel circulation flow velocities to assuresatisfactory water removal from PEM fuel cells are readily achieved.

[0108] While recycle of cathode gas has benefits as discussed above, itwill be understood that the invention may also be practiced without anysuch recycle feature, so that the cathode gas from cathode exit 270 mayalternatively be either discharged to atmosphere or else removed toanother use such as assisting combustion within a fuel processor.

[0109] Another variation is to operate the oxygen PSA unit to deliveroxygen at a relatively high concentration (e.g. in the range of 60% to95%, or more preferably 70% to 90% oxygen concentration), whilebypassing a fraction of the compressed air feed from conduit 216 pastthe PSA module to blend directly with product oxygen in conduit 70,conduit 283 or conduit 253. In this approach, the blended bypass air andPSA oxygen product (plus any recycle cathode gas from cathode exit port270) may have a mixed oxygen concentration in the range of e.g. 30% to50% so that a substantial benefit of partial oxygen enrichment over thefuel cell cathode is provided, while the size and power consumption ofthe PSA unit is reduced.

[0110] Turning to FIG. 10, an oxygen-separating PSA-based fuel cellsystem is shown, similar to the fuel cell system in FIG. 9, but with acountercurrent blowdown expander driving a free rotor exhaust vacuumpump. Thus, in FIG. 9 dashed line 290 represents an optional feed airbypass conduit 290 with a flow control valve 291, communicating betweencompressed air feed conduit 216 and conduit 283 in the cathode recycleloop. In the embodiment of FIG. 10, shaft 222 coupling thecountercurrent blowdown expander 221 to feed compressor 201 has beenremoved. Instead, vacuum pump 301 is used to depress the low pressure ofthe cycle below atmospheric pressure, drawing nitrogen-enriched wastegas from heavy product exhaust compartment 61 via conduit 246 andoptional heater 302. Pump 301 is powered by countercurrent blowdownexpander 304 expanding countercurrent blowdown gas from firstcountercurrent blowdown manifold 57 via conduit 240 and optional heater241. Vacuum pump 301 and expander 304 are coupled by shaft 305, andtogether constitute a free rotor vacuum pump assembly 306. Such a freerotor vacuum pump offers attractive advantages of efficiency and capitalcost. Alternatively, a motor could be coupled to an extension of shaft305.

[0111] The countercurrent blowdown gas from second countercurrentblowdown manifold 59 exits that manifold at a pressure which issubstantially atmospheric or slightly greater according to the amount ofthrottling restriction associated with conduit 244.

[0112]FIG. 11

[0113]FIG. 11 shows a fuel cell-based electrical current generatingsystem, similar to the electrical current generating system of FIG. 9,but without light reflux energy recovery, and with a portion of oxygenenriched gas discharged from the fuel cell cathode being used for apressurization step. The illustrative four stages of light refluxpressure letdown are achieved irreversibly over adjustable orifices 350,351, 352 and 353, which respectively connect conduits 224 and 227, 228and 231, 232 and 235, and 236 and 239. Orifices 350, 351, 352 and 353are actuated through linkage 354 by actuator(s) 355. Adjustment of theorifices is desirable to enable turndown of the PSA apparatus tooperation at reduced cycle frequency and reduced flow rates when thefuel cell power plant is operated at part load.

[0114] The fuel cell has a cathode recycle loop defined (in the loopflow direction) by water condensate separator 360, conduit 361 conveyingenriched oxygen to cathode channel inlet 261, cathode channel 262,conduit 362 conveying cathode exhaust gas from cathode channel exit 270to cathode recycle conduit 365 including cathode recycle blower 363 topressurize the cathode recycle gas for admission to condensate separator360. Separator 360 removes fuel cell water exhaust condensate from thecathode recycle loop, while also humidifying the dry concentrated oxygenadmitted from the PSA system conduit from conduit 218.

[0115] A portion of the cathode exhaust is removed from the conduit 362by conduit 371, branching from cathode recycle conduit 365. This portionof the cathode exhaust gas is recycled to the feed end of the PSA (oralternatively vacuum-PSA) apparatus, and is conveyed by conduit 371 towater condensate separator 373 and thence to first pressurizationmanifold 48 communicating to the first valve face 21. A throttle valve373 may be provided in conduit 371 to provide a pressure letdown asrequired from the pressure at cathode exit 270 to first pressurizationmanifold 48.

[0116] Recycling a portion of the cathode exhaust gas to the PSA unitfeed has several advantages, including (1) reducing the volume of feedgas to be compressed, (2) eliminating the requirement to purge anycathode exhaust gas from the cathode loop, and (3) recovering some wasteenergy from the fuel cell cathode loop by using this gas to helppressurize the fuel cell from the feed end. This oxygen rich gas must beadmitted to the feed end of the PSA unit, because it is saturated withwater vapor which would deactivate the adsorbent if admitted directly tothe second valve face at the product end. By introducing it to the feedend of the beds after the low pressure step and before any directpressurization with feed air, a favorable concentration profile isestablished since this gas is richer in oxygen than feed air, but alsocontains a greater load of impurities than the product oxygen-enrichedgas.

[0117] Because argon is concentrated with oxygen by the PSA unit, argonwill be concentrated both within the cathode loop and in the PSAenriched oxygen product in this embodiment. If no cathode purge isprovided, argon can only exit the system through the exhaust of the PSAunit. Since the PSA unit typically achieves about 60% recovery of oxygenand argon when ordinary air is used as the only feed for pressurizationto the first valve face, about 40% of argon admitted with feed gas maybe exhausted in each cycle. The fractional elimination of recycle argonintroduced with initial feed pressurization steps will be lower, sincethe main feed is introduced subsequently to push the recycle argondeeper into the absorbers. Hence, a small amount of purge from thecathode loop may be desirable. Cathode exhaust gas recycle to the PSAunit feed may also be blended directly with feed air introduced at thesame or lower pressure as the cathode channel exit 270.

[0118]FIG. 12

[0119]FIG. 12 shows a fuel-cell based electrical current generatingsystem 400, according to a second embodiment of the present invention,comprising a fuel cell 402, an oxygen-generating PSA system 404, and ahydrogen gas production system 406. The fuel cell comprises an anodechannel 408 including an anode gas inlet 410 and an anode gas outlet412, a cathode channel 414 including a cathode gas inlet 416 and acathode gas outlet 418, and a PEM 420 in communication with the anodechannel 408 and the cathode channel 414 for facilitating ion exchangebetween the anode channel 408 and the cathode channel 414.

[0120] The oxygen-PSA system 404 extracts oxygen gas from feed air, andcomprises a rotary module 10, and a compressor 422 for deliveringpressurized feed air to the feed compartments 424 of the rotary module10. Preferably, the oxygen-PSA system 404 includes a vacuum pump 426 (oralternatively countercurrent blowdown expander) coupled to thecompressor 422 for withdrawing nitrogen-enriched gas as heavy productgas from the blowdown compartments 428 of the rotary module 10. Theoxygen-PSA system 404 also includes a light product gas functioncompartment 430 coupled to the cathode gas inlet 416 for deliveringoxygen-enriched gas to the cathode channel 414. Cathode recycle may beprovided as in the embodiments of FIGS. 9-11.

[0121] The hydrogen gas production system 406 comprises ahydrogen-generating PSA system 432, and a fuel processor reactor 434coupled to the hydrogen-PSA system 432 for supplying a first hydrogengas feed to the hydrogen-PSA system 432. The hydrogen-PSA system 432comprises a rotary module 10 including a first feed gas compartment 436for receiving a first hydrogen gas feed from the reactor 434, apressurization compartment 438 for receiving a hydrogen gas feed fromthe anode gas outlet 412, a light product compartment 440 for deliveringhydrogen gas to the anode gas inlet 410, and a blowdown compartment 441for delivering tail gas as heavy product gas to the reactor 434.Preferably the hydrogen-PSA system 432 includes a vacuum pump 442 (oralternately a countercurrent blowdown expander) provided between theblowdown compartment 441 and the reactor 434 for extracting the tail gasfrom the blowdown compartment 441.

[0122] According to the purity level of the hydrogen gas recycled fromthe anode gas exit 412, pressurization compartment 438 may cooperatewith either the first or second valve of the rotary module, the latterbeing preferred if the purity of this stream is relatively high. Thehydrogen-PSA system 432 may also include a heavy reflux compressor 443delivering heavy reflux gas to a second feed gas compartment 444 toimprove the fractional recovery of hydrogen gas. The calorific fuel gasrequirements of the hydrogen gas production system 406 will determinethe correct recovery of hydrogen gas.

[0123] The reactor 434 comprises a steam reformer 445, including aburner 446 and catalyst tubes (not shown), and a water gas shift reactor448. The burner 446 includes a first burner inlet 450 for receiving thetail gas from the blowdown compartment 442, and a second burner inlet452 for receiving air or humid oxygen-enriched gas from the cathodechannel 414. The steam reformer 444 is supplied through a fuel inlet 454with a hydrocarbon fuel, such as methane gas, plus water at a feedpressure which is the working pressure of the fuel cell plus anallowance for pressure drops through the system 406. The fuel ispreheated and steam is generated by heat exchanger 455, recovering heatfrom the flue gas of burner 446. The methane fuel gas and steam mixtureis them passed through the catalyst tubes, while the tail gas and theoxygen-enriched gas are burned in the burner 446 to elevate thetemperature of the methane fuel gas mixture to the temperature necessary(typically 800° C.) for conducting endothermic steam reforming reactionsof the methane fuel gas mixture:

CH₄+H₂O−CO+3H₂

CH₄+2H₂O−CO₂+4H₂

[0124] The resulting syngas (approximately 70% H₂, with equal amounts ofCO and CO₂ as major impurities, and unreacted CH₄ and N₂ as minorimpurities) is cooled to about 250° C., and then passed to the water gasshift reactor 448 for reacting most of the CO with steam to produce moreH₂ and CO₂:

CO+H₂O−CO₂+H₂

[0125] The resulting gas reactants are then conveyed to the first feedcompartment 436 of the hydrogen-PSA system 432 for hydrogenpurification, with the heavy product tail gas being returned to thesteam reformer 434 form the blowdown compartment 442 for combustion inthe burner 446.

[0126] In one variation, the reactor 434 comprises a partial oxidationreactor, and instead of the methane gas mixture being steam reformed,the methane gas mixture is reacted in the partial oxidation reactor witha portion of the humid oxygen-enriched gas received from the cathodechannel 414, through an optional conduit 456, for partial oxidation ofthe methane gas:

CH₄+½O₂−CO+2H₂

[0127] The resulting syngas is again cooled to about 250° C., and thenpassed to the water gas shift reactor 448 for reacting most of the COwith steam to produce more H₂ and CO₂:

CO+H₂O−CO₂+H₂

[0128] The resulting gas reactants are then conveyed to the first feedcompartment 436 of the hydrogen-PSA system 432 for hydrogenpurification, with the heavy product tail gas being purged from thehydrogen-PSA system 432.

[0129] In another variation, the reactor 434 comprises as autothermalreformer and a water gas shift reactor 448, and instead of the methanegas mixture being endothermically steam reformed or exothermicallypartially oxidized, the methane gas mixture is reacted in theautothermal reformer by a thermally balanced combination of thosereactions, followed by reaction in the water gas shift reactor 448.Since the hydrogen-PSA heavy product tail gas will always have some fuelvalue even in the limit of very high heavy reflux, a burner 446 would beprovided for efficiently preheating air and or fuel feeds to anyautothermal reactor. Unless the fuel processing reactions include anendothermic reforming component as an energy-efficient sink for tail gasfuel combustion, another economic use (as in embodiment of FIG. 13)should be provided if the net fuel processing reactions are highlyendothermic, as in the case of simple partial oxidation.

[0130] Oxygen enrichment autothermal or partial oxidation fuel processoradvantageously reduces the heating load of reactants entering thereaction chamber, and also reduces the cooling load of hydrogen-richproduct gases delivered to the hydrogen PSA unit and the fuel cellanode, owing to the depletion of nitrogen from those gas streams. Afurther advantage of the present invention is the ability of thehydrogen PSA unit to remove ammonia in addition to carbon monoxide andhydrogen sulfide, which contaminants are all extremely detrimental toPEM fuel cell performance and life expectancy. Ammonia may be formed infuel processors where hydrocarbons are catalytically reformed tohydrogen in the presence of any atmospheric nitrogen. The oxygen PSAreduces this problem by front-end removal of nitrogen, while thehydrogen PSA removes any residual traces of ammonia.

[0131]FIG. 13

[0132] It would be apparent that a deficiency of the electrical currentgenerating system 400 relates to the necessity of driving the compressor422 and the vacuum pumps 426, 444 with a portion of the electrical powergenerated by the fuel cell. FIG. 13 shows a fuel cell based electricalcurrent generating system 500, which addresses this deficiency.

[0133] The electrical current generating system 500 is substantiallysimilar to the electrical current generating system 400, comprising thefuel cell 402, an oxygen-generating PSA system 504, and a hydrogen gasproduction system 506. The oxygen-PSA system 504 extracts oxygen gasfrom feed air, and comprises a rotary module 10, a compressor 522 fordelivering pressurized feed air to the feed compartments 524 of therotary module 10, a combustion expander 523 coupled to the compressor522, a starter motor (not shown) coupled to the compressor 522, and alight product gas function compartment 530 coupled to the cathode gasinlet 416 for delivering oxygen-enriched gas to the cathode channel 414.The oxygen-PSA system 504 may also have a countercurrent blowdown orheavy product exhaust compartment 531 cooperating with a vacuum pumpand/or expander, as illustrated in previous embodiments.

[0134] The hydrogen gas production system 506 comprises ahydrogen-generating PSA system 532, and a reactor 534 coupled to thehydrogen-PSA system for supplying a first hydrogen gas feed to thehydrogen-PSA system 532. The hydrogen-PSA system 532 comprises a rotarymodule 10 including a first feed gas compartment 536 for receiving afirst hydrogen gas feed from the steam reformer 534, a pressurizationcompartment 538 (communicating with either the first or second valve)for receiving a second hydrogen gas feed from the anode gas outlet 412,a light product compartment 540 for delivering hydrogen gas to the anodegas inlet 410, and a blowdown compartment 541 for delivering tail gas asheavy product fuel gas to the reactor 534. As in previous embodiments,the blowdown compartment 541 may cooperate with an exhaust vacuum pumpand/or expander (not shown) for extracting the tail gas from theblowdown compartment 541.

[0135] The reactor 534 comprises an autothermal reformer 544, a burner546, and a water gas shift reactor 548. The burner 546 includes heatertubes 549, a first burner inlet 550 for receiving the tail gas from theblowdown compartment 542, and a second burner inlet 552 for receivingcompressed air from the compressor 522 second stage. As will be apparentfrom FIG. 13, the compressor 522 second stage compresses a portion ofthe feed air which is not delivered to the oxygen-generating PSA system504.

[0136] The expander 523 and the compressor 522 together comprise a gasturbine, and expands combustion product gas emanating from the burner546 so as to increase the pressure of feed air to the feed compartments524. As will be appreciated, the thermal energy of combustion of thehydrogen-PSA tail gas is used to drive the fuel cell accessory gaspurification and compression machinery. As shown in FIG. 13, additionalfeed gas compression energy may be obtained from the exothermic heat ofreaction of the water gas shift reactor 548 through preheat exchangers555.

[0137] The autothermal reformer 544 is supplied through a fuel inlet 554with a hydrocarbon fuel gas, such as methane gas and, in the exampleshown, is reacted with oxygen-enriched gas received under pressure fromthe cathode channel 414 through booster blower 556. Cathode recycle maynot be justified, or at least may be reduced, if the oxygen-enriched gasdelivered from the cathode exit can be used advantageously for fuelprocessing (to reduce nitrogen load and enhance combustion). Theresultant syngas is then cooled, and then passed to the water gas shiftreactor 548 for reacting most of the CO with steam to produce more H₂and CO₂. The resulting gas reactants are then conveyed to the first feedcompartment 536 of the hydrogen-PSA system 532 for hydrogenpurification.

[0138] In some embodiments, at least a portion of the cathode exhaustgas (which is still enriched in oxygen relative to ambient air, andcarries fuel cell exhaust water and fuel cell waste heat) is returned tothe inlet of an autothermal or partial oxidation fuel processor (orreformer) for reacting a hydrocarbon fuel with oxygen and steam in orderto generate raw hydrogen or syngas. The oxygen reacts autothermally witha portion of the fuel to produce carbon monoxide and heat which furthersreaction of remaining fuel with steam to generate hydrogen. Excess steamhelps prevent any coking in the reformer or fuel processor, andsubsequently reacts at lower temperature with the carbon monoxide in awater gas shift reactor to generate more hydrogen mixed with wastecarbon dioxide. Residual carbon monoxide, the carbon dioxide and anyother impurities can then be removed by a hydrogen PSA unit according tothe invention.

[0139] Delivery of still enriched oxygen gas from the fuel cell cathodeto the inlet of the fuel processor (1) reduces the inert load ofnitrogen entrained with atmospheric air as oxidant, (2) enhancescirculation velocities within the fuel cell cathode channel foreffective water removal, (3) directly recovers exhaust water from thecathode for the fuel processor in direct accordance with water demandfor fuel processing, (4) delivers that water largely in vapor form toavoid costly condensation and revaporization steps, (5) delivers somefuel cell waste heat usefully to the fuel processor inlet, and (3)enhances overall system efficiency through desirable thermalintegration.

[0140]FIG. 14

[0141] Embodiment 600 illustrates further aspects of the invention. Foralkaline fuel cells, the crucial problem is removal of CO₂ from bothfeed oxidant and hydrogen streams. The oxygen-PSA and hydrogen-PSAsystems of this invention as described above will remove CO₂ veryeffectively, since CO₂ is much more strongly adsorbed than otherpermanent gas impurities. Oxygen enrichment is beneficial for all typesof fuel cells in increasing voltage efficiency, although not usuallyjustified except at high current densities. Alkaline fuel cells can usean under-sized oxygen-PSA for very effective carbon dioxide removalalong with modest oxygen enrichment, or may use the same PSA device withan adsorbent lacking nitrogen/oxygen selectivity (e.g. activated carbon,or high silica zeolites) for carbon dioxide clean-up without oxygenenrichment. The rotary PSA module and compression machinery of thisinvention for entirely suitable for this role.

[0142] Alkaline fuel cells operating on ambient air feed typicallyoperate near atmospheric pressure, at about 70° C. Under suchconditions, the water vapor saturated cathode exhaust stream ofnitrogen-enriched air serves to remove fuel cell product water whilemaintaining electrolyte water balance. Operation of alkaline fuel cellsat higher temperature may be desirable for high efficiency with lesscostly electrocatalyst materials, or else for thermal integration to amethanol reformer using fuel cell waste heat to vaporize reactants andeven drive the endothermic reaction. But with increasing stack exhausttemperatures, operation with ambient air composition may rapidly becomeimpracticable. At higher temperatures, the nitrogen rich cathode exhaustsimply carries too much water vapor out of the system, unless the totalpressure is uneconomically raised or else a condenser for water recoveryis included.

[0143] With oxygen enrichment, the volume of the cathode exhaust can beadjusted to achieve water balance for any alkaline fuel cell. Reasonablelow stack working pressures become practicable, e.g. about 3 atmospheresfor a cathode exit temperature of 120° C. If oxygen enrichment iscarried out to the full capability of oxygen-PSA, e.g. approaching 95%oxygen purity, the cathode exhaust stream becomes dry steam with amodest concentration of permanent gases. This steam product may beuseful for diverse applications, including fuel processing ofhydrocarbon feedstocks to generate hydrogen.

[0144] Embodiment 600 shows an oxygen-PSA (also performing CO₂ removal)as shown in FIG. 12. The hydrogen side of the system is simplified inthis example to show only the anode gas inlet of pure hydrogen. Oxygenat more than 90% purity is supplied to the cathode gas inlet 416, whileconcentrated water vapor is delivered from cathode gas exit 418 andconveyed directly to steam expander 610. Expander 610 discharges tovacuum condenser 612, from which liquid condensate is removed by pump614, while the permanent gas overheads are withdrawn through conduit byvacuum pump 426 of the oxygen-PSA. Expander 610 may assist motor 616 todrive the compression machinery of the oxygen-PSA, thus improvingoverall efficiency of the fuel power plant by approximately 2 to 3%.

[0145] A final aspect of the invention (for any type of fuel cell) isthe optional provision of light product gas accumulators for the PSAunits, and particularly for the oxygen-PSA as illustrated in FIG. 14.Oxygen product accumulator 660 includes an oxygen storage vessel 661charged from the light product compartment 430 through non-return valve662, at substantially the upper pressure of the PSA process oroptionally at an elevated pressure generated by a small accumulatorcharging compressor 663. A peaking oxygen delivery valve 665 and abackflush valve 666 are provided on either side of non-return valve 667so as to enable oxygen delivery from the storage vessel respectivelyforward to the fuel cell cathode inlet or backward to the oxygen-PSAunit.

[0146] The oxygen storage vessel is charged during normal operation,particularly during intervals of stand-by or idling when the oxygen-PSAattains highest oxygen purity. The optional charging compressor may beoperated when the plant is idling, or (in vehicle applications) as anenergy load application of regenerative braking. The peaking oxygendelivery valve 665 is opened during intervals of peak power demand, soas to increase supply of concentrated oxygen to the cathode when mostneeded. If the oxygen accumulator is large enough, the oxygen-PSAcompressor 422 and vacuum pump 426 could be idled during brief intervalsof peak power demand, so as to release the power normally consumed byinternal accessories to meet external demand. Then, the size of the fuelcell stack (in a power plant required to meet occasional specified peakpower levels) can be reduced for important cost savings.

[0147] When the fuel cell power plant is shut down, the oxygen-PSAcompressor 422 is stopped first to drop the internal pressure for aninitial blowdown of all absorbers. Then, backflush valve 666 is openedto release a purging flow of oxygen to displace adsorbed nitrogen andsome adsorbed water vapor from the absorbers over a short time interval.The absorbers are then left precharged with dry oxygen at atmosphericpressure, thus enabling fast response of the oxygen-PSA for the nextplant start-up.

[0148] FIGS. 15-21

[0149]FIG. 15 shows a rotary PSA module 701 configured for axial flowand particularly suitable for smaller scale oxygen generation andhydrogen purification. Module 701 includes a number “N” of adsorbers 703in adsorber housing body 704. Each adsorber has a first end 705 and asecond end 706, with a flow path therebetween contacting anitrogen-selective adsorbent. The adsorbers are deployed in anaxisymmetric array about axis 707 of the adsorber housing body. Thehousing body 704 is in relative rotary motion about axis 707 with firstand second functional bodies 708 and 709, being engaged across a firstvalve face 710 with the first functional body 708 to which feed air issupplied and from which nitrogen-enriched air is withdrawn as the heavyproduct, and across a second valve face 711 with the second functionalbody 709 from which oxygen-enriched air is withdrawn as the lightproduct.

[0150] In preferred embodiments as particularly depicted in FIGS. 15-21,the adsorber housing 704 rotates and shall henceforth be referred to asthe adsorber rotor 704, while the first and second functional bodies arestationary and together constitute a stator assembly 712 of the module.The first functional body shall henceforth be referred to as the firstvalve stator 708, and the second functional body shall henceforth bereferred to as the second valve stator 709.

[0151] In the embodiment shown in FIGS. 15-21, the flow path through theadsorbers is parallel to axis 707, so that the flow direction is axial,while the first and second valve faces are shown as flat annular discsnormal to axis 707. However, more generally the flow direction in theadsorbers may be axial or radial, and the first and second valve facesmay be any figure of revolution centred on axis 707. The steps of theprocess and the functional compartments to be defined will be in thesame angular relationship regardless of a radial or axial flow directionin the adsorbers.

[0152] FIGS. 15-21 are cross-sections of module 701 in the planesdefined by arrows 712-713, 714-715, and 716-717. Arrow 720 in eachsection shows the direction of rotation of the rotor 704.

[0153]FIG. 16 shows section 712-713 across FIG. 15, which crosses theadsorber rotor. Here, “N”=72. The adsorbers 703 are mounted betweenouter wall 721 and inner wall 722 of adsorber rotor 704. Each adsorbercomprises a rectangular flat pack 703 of adsorbent sheets 723, withspacers 724 between the sheets to define flow channels here in the axialdirection. Separators 725 are provided between the adsorbers to fillvoid space and prevent leakage between the adsorbers. Other preferredconfigurations for the adsorber module may be provided by forming theadsorbent sheets and intervening spacers in trapezoidal packs or spiralrolls constituting each adsorber.

[0154] Alternatively the entire adsorber rotor may be formed as a spiralroll of one adsorbent sheet or a plurality of adsorbent sheets, thespiral roll formed concentric with the axis 707 and with spacers betweenadjacent layers of the spirally rolled adsorbent sheet(s), and with atleast some of the spacers at narrow angular intervals extending alongthe entire length between the first and second ends as barriers totransverse flow, so as to partition the spiral roll into many channels,each of which serves as a distinct adsorber. The first and second endsof the spiral roll would directly coincide with the first and secondvalve faces respectively.

[0155] The adsorbent sheets comprise a reinforcement material, inpreferred embodiments glass fibre, metal foil or wire mesh, to which theadsorbent material is attached with a suitable binder. For airseparation to produce enriched oxygen, typical adsorbents are X, A orchabazite type zeolites, typically exchanged with lithium, calcium,strontium, magnesium and/or other cations, and with optimizedsilicon/aluminium ratios as well known in the art. The zeolite crystalsare bound with silica, clay and other binders, or self-bound, within theadsorbent sheet matrix.

[0156] Satisfactory adsorbent sheets have been made by coating a slurryof zeolite crystals with binder constituents onto the reinforcementmaterial, with successful examples including nonwoven fibreglass scrims,woven metal fabrics, and expanded aluminium foils. Spacers are providedby printing or embossing the adsorbent sheet with a raised pattern, orby placing a fabricated spacer between adjacent pairs of adsorbentsheets. Alternative satisfactory spacers have been provided as wovenmetal screens, non-woven fibreglass scrims, and metal foils with etchedflow channels in a photolithographic pattern.

[0157] Typical experimental sheet thicknesses have been 150 microns,with spacer heights in the range of 100 to 150 microns, and adsorberflow channel length approximately 20 cm. Using X type zeolites,excellent performance has been achieved in oxygen separation from air atPSA cycle frequencies in the range of 30 to 150 cycles per minute.

[0158]FIG. 17 shows the porting of rotor 704 in the first and secondvalve faces respectively in the planes defined by arrows 714-715, and716-717. An adsorber port 730 provides fluid communication directly fromthe first or second end of each adsorber to respectively the first orsecond valve face.

[0159]FIG. 18 shows the first stator valve face 800 of the first stator708 in the first valve face 710, in the plane defined by arrows 714-715.Fluid connections are shown to a feed compressor 801 inducting feed airfrom inlet filter 802, and to an exhauster 803 deliveringnitrogen-enriched second product to a second product delivery conduit804. Compressor 801 and exhauster 803 are shown coupled to a drive motor805.

[0160] Arrow 720 indicates the direction of rotation by the adsorberrotor. In the annular valve face between circumferential seals 805 and806, the open area of first stator valve face 800 ported to the feed andexhaust compartments is indicated by clear angular segments 811-816corresponding to the first functional ports communicating directly tofunctional compartments identified by the same reference numerals811-816. The substantially closed area of valve face 800 betweenfunctional compartments is indicated by hatched sectors 818 and 819which are slippers with zero clearance, or preferably a narrow clearanceto reduce friction and wear without excessive leakage. Typical closedsector 818 provides a transition for an adsorber, between being open tocompartment 814 and open to compartment 815. Gradual opening is providedby a tapering clearance channel between the slipper and the sealingface, so as to achieve gentle pressure equalization of an adsorber beingopened to a new compartment. Much wider closed sectors (e.g. 819) areprovided to substantially close flow to or from one end of the adsorberswhen pressurization or blowdown is being performed from the other end.

[0161] The feed compressor provides feed air to feed pressurizationcompartments 811 and 812, and to feed production compartment 813.Compartments 811 and 812 have successively increasing working pressures,while compartment 813 is at the higher working pressure of the PSAcycle. Compressor 801 may thus be a multistage or split streamcompressor system delivering the appropriate volume of feed flow to eachcompartment so as to achieve the pressurization of adsorbers through theintermediate pressure levels of compartments 811 and 812, and then thefinal pressurization and production through compartment 813. A splitstream compressor system may be provided in series as a multistagecompressor with interstage delivery ports; or as a plurality ofcompressors or compression cylinders in parallel, each delivering feedair to the working pressure of a compartment 811 to 813. Alternatively,compressor 801 may deliver all the feed air to the higher pressure, withthrottling of some of that air to supply feed pressurizationcompartments 811 and 812 at their respective intermediate pressures.

[0162] Similar, exhauster 803 exhausts nitrogen-enriched heavy productgas from countercurrent blowdown compartments 814 and 815 at thesuccessively decreasing working pressures of those compartments, andfinally from exhaust compartment 816 which is at the lower pressure ofthe cycle. Similarly to compressor 801, exhauster 803 may be provided asa multistage or split stream machine, with stages in series or inparallel to accept each flow at the appropriate intermediate pressuredescending to the lower pressure.

[0163] In the example embodiment of FIG. 18, the lower pressure isambient pressure, so exhaust compartment 816 exhaust directly to heavyproduct delivery conduit 804. Exhauster 803 thus provides pressureletdown with energy recovery to assist motor 805 from the countercurrentblowdown compartments 814 and 815. For simplicity, exhauster 803 may bereplaced by throttling orifices as countercurrent blowdown pressureletdown means from compartments 814 and 815.

[0164] In some preferred embodiments, the lower pressure of the PSAcycle is subatmospheric. Exhauster 803 is then provided as a vacuumpump, as shown in FIG. 19. Again, the vacuum pump may be multistage orsplit stream, with separate stages in series or in parallel, to acceptcountercurrent blowdown streams exiting their compartments at workingpressures greater than the lower pressure which is the deepest vacuumpressure. In FIG. 19, the early countercurrent blowdown stream fromcompartment 814 is released at ambient pressure directly to heavyproduct delivery conduit 804. If for simplicity a single stage vacuumpump were used, the countercurrent blowdown stream from compartment 815would be throttled down to the lower pressure over an orifice to jointhe stream from compartment 816 at the inlet of the vacuum pump.

[0165]FIGS. 20 and 21 shows the second stator valve face, at section716-717 of FIG. 15. Open ports of the valve face are second valvefunction ports communicating directly to a light product deliverycompartment 821; a number of light reflux exit compartments 822, 823,824 and 825; and the same number of light reflux return compartments826, 827, 828 and 829 within the second stator. The second valvefunction ports are in the annular ring defined by circumferential seals831 and 832. Each pair of light reflux exit and return compartmentsprovides a stage of light reflux pressure letdown, respectively for thePSA process functions of supply to backfill, full or partial pressureequalization, and cocurrent blowdown to purge.

[0166] Illustrating the option of light reflux pressure letdown withenergy recovery, a split stream light reflux expander 840 is shown inFIGS. 15 and 20 to provide pressure let-down of four light reflux stageswith energy recovery. The light reflux expander provides pressurelet-down for each of four light reflux stages, respectively betweenlight reflux exit and return compartments 822 and 829, 823 and 828, 824and 827, and 825 and 826 as illustrated. The light reflux expander 840may power a light product booster compressor 845 by drive shaft 846,which delivers the oxygen enriched light product to oxygen deliveryconduit 847 and compressed to a delivery pressure above the higherpressure of the PSA cycle. Illustrating the option of light refluxpressure letdown with energy recovery, a split stream light refluxexpander 840 is provided to provide pressure let-down of four lightreflux stages with energy recovery. The light reflux expander serves aspressure let-down means for each of four light reflux stages,respectively between light reflux exit and return compartments 822 and829, 823 and 828, 824 and 827, and 825 and 826 as illustrated.

[0167] Light reflux expander 840 is coupled to a light product pressurebooster compressor 845 by drive shaft 846. Compressor 845 receives thelight product from conduit 725, and delivers light product (compressedto a delivery pressure above the higher pressure of the PSA cycle) todelivery conduit 250. Since the light reflux and light product are bothenriched oxygen streams of approximately the same purity, expander 840and light product compressor 845 may be hermetically enclosed in asingle housing which may conveniently be integrated with the secondstator as shown in FIG. 15. This configuration of a “turbocompressor”oxygen booster without a separate drive motor is advantageous, as auseful pressure boost of the product oxygen can be achieved without anexternal motor and corresponding shaft seals, and can also be verycompact when designed to operate at very high shaft speeds.

[0168]FIG. 21 shows the simpler alternative of using a throttle orifice850 as the pressure letdown means for each of the light reflux stages.

[0169] Turning back to FIG. 15, compressed feed air is supplied tocompartment 813 as indicated by arrow 825, while nitrogen enriched heavyproduct is exhausted from compartment 817 as indicated by arrow 826. Therotor is supported by bearing 860 with shaft seal 861 on rotor driveshaft 862 in the first stator 708, which is integrally assembled withthe first and second valve stators. The adsorber rotor is driven bymotor 863 as rotor drive means.

[0170] As leakage across outer circumferential seal 831 on the secondvalve face 711 may compromise enriched oxygen purity, and moreimportantly may allow ingress of atmospheric humidity into the secondends of the adsorbers which could deactivate the nitrogen-selectiveadsorbent, a buffer seal 870 is provided to provide more positivesealing of a buffer chamber 871 between seals 831 and 871. A desiccant873 (e.g. alumina, silica gel, sodium hydroxide, potassium hydroxide,magnesium perchlorate, barium oxide, phosphorous pentoxide, calciumchloride, calcium sulfate, calcium oxide, or magnesium oxide) may beincluded in buffer chamber 871 to provide more moisture protection. Eventhough the working pressure in some zones of the second valve face maybe subatmospheric (in the case that a vacuum pump is used as exhauster803), buffer chamber is filled with dry enriched oxygen product at abuffer pressure positively above ambient pressure. Hence, minor leakageof dry oxygen outward may take place, but humid air may not leak intothe buffer chamber. In order to further minimize leakage and to reduceseal frictional torque, buffer seal 871 seals on a sealing face 872 at amuch smaller diameter than the diameter of circumferential seal 831.Buffer seal 870 seals between a rotor extension 875 of adsorber rotor704 and the sealing face 872 on the second valve stator 709, with rotorextension 875 enveloping the rear portion of second valve stator 709 toform buffer chamber 871. A stator housing member 880 is provided asstructural connection between first valve stator 8 and second valvestator 709.

[0171]FIG. 22

[0172]FIG. 22 shows an axial section of a rotary PSA embodiment, inwhich the adsorbers and adsorber body housing 904 are stationary, whilethe first and second distributor valve bodies are first valve rotor 908and second valve rotor 909 respectively engaged with first valve face910 and second valve face 911. The first valve rotor 908 is driven bymotor 1063 through shaft 1062, while the second valve rotor 9 is drivenby connecting shaft 1110. As the arrows 720 in FIGS. 16-21 indicate thedirection of relative motion of the adsorber housing 904 relative to thedistributor valve bodies, the rotation of valve rotors 908 and 909 forthe stationary adsorber embodiment of FIG. 22 may be in the oppositedirection to arrows 720 when referred to the stationary housing 904. Thefirst valve rotor 908 is installed within first valve housing 1112, andsecond valve rotor 909 is installed within second valve housing 214.Housings 1112 and 1114 are assembled with adsorber housing 904 to form acomplete pressure containment enclosure for the PSA module 901.

[0173] Alternative valve configurations and pressure balancing devicesfor the first and second rotating distributor valves for embodimentswith stationary adsorbers are disclosed by Keefer et al in U.S. Pat. No.6,063,161, the disclosure of which is incorporated herein.

[0174] For all externally connected flow functions where feed isprovided to the first valve body, exhaust is withdrawn from the firstvalve body, or gas is withdrawn from or returned to the second valvebody, fluid transfer chambers are provided for each such flow function,in order to establish fluid communication from the housing to the rotorfor that function. Each fluid transfer chamber is an annular cavity inthe valve rotor or its housing, providing fluid communication at allangular positions of the rotor between a functional compartment in therotor and the corresponding external conduit connected to the housing.Rotary seals must be provided for each such fluid transfer chamber toprevent leakage. A particular advantage of rotary adsorber embodimentsis the elimination of such fluid transfer chambers and associated seals,since in those embodiments the first and second valve bodies arestationary and may be connected directly to external flow functions.

[0175] A feed transfer chamber 1120 communicates between feed conduit1081 and functional compartment 1013 in the first valve rotor 908, andan exhaust transfer chamber 1122 communicates to exhaust conduit 1082and functional compartment 1016 in the first valve rotor 908. Transferchambers 1120 and 1122 are separated by rotary seal 1124. Thisconfiguration is suitable for a single stage feed compressor 1001 and asingle stage exhauster 1003. Narrow clearance gaps in first valve face910 may extend from compartment 1013 over the annular sectorscorresponding to compartments 812 and 811 in FIGS. 18 and 19, and fromcompartment 1016 over the annular sectors corresponding to compartments815 and 814 in FIGS. 18 and 19, so as to provide throttling for gentlepressurization and depressurization of each adsorber being opened tocompartments 1013 or 1016. While additional transfer chambers could beprovided for additional compression or exhaust stages, it will beappreciated that this complication could be avoided with rotary adsorberembodiments.

[0176] A product transfer chamber 1126 communicates between productdelivery conduit 1047 and functional compartment 1021 in the secondvalve rotor 909. Rotary seal 1127 is provided for transfer chamber 1126.Additional transfer chambers could be provided in pairs for exit andreturn of each light reflux stage. This may be necessary if a lightreflux expander 840 is provided as shown in FIG. 20. However, it will bemuch simpler in the stationary adsorber embodiments to avoid fluidtransfer between the second valve rotor 909 and its housing 1114 forlight reflux stages. For stationary adsorber embodiments, it will thusbe preferred to use throttle orifices 850 for pressure let-down of eachlight reflux stage as shown in FIG. 21, with these orifices 850installed within rotor 909 so that no fluid transfer between rotor 909and housing 1114 is required for light reflux. One such orifice 1050 isshown in FIG. 22, with the connection to light reflux exit compartment1025 being out of the sectional plane and accordingly not shown in theview of FIG. 22.

[0177] Axial Flow Oxygen Enrichment PSA Unit

[0178] The specific productivity and the yield of an axial flow rotaryoxygen enrichment PSA module similar to module 701 of FIG. 15 wasmeasured with air feed at 30° C. The module had a total volume of 18 L(not including the compressor, the vacuum pump, and the rotor drivemotor), and a contained adsorber volume of 8.2 L. Specific productivityis defined as normal liters of contained product oxygen delivered perhour per liter of adsorber volume, and yield is defined as fractionalrecovery of oxygen contained in the product from oxygen contained in thefeed air.

[0179] Operating in a vacuum-PSA mode at a cycle frequency of 100cycles/minute with feed air compressed to 1.5 bars absolute and vacuumexhaust at 0.5 bars absolute, oxygen product at 70% purity was obtainedwith specific productivity of 1500 NL/L-hour, at a yield of 47%.

[0180] Operating in a vacuum-PSA mode at a cycle frequency of 100cycles/minute with feed air compressed to 1.5 bars absolute and vacuumexhaust at 0.5 bars absolute, oxygen product at 70% was obtained withspecific productivity improved to 1650 NL/L-hour and yield improved to50.5%.

[0181] Operating in a vacuum-PSA mode at a cycle frequency of 100cycles/minute with feed air compressed to 1.7 bars absolute and vacuumexhaust at 0.32 bars absolute, oxygen product at 80% purity was obtainedwith a specific productivity of 2500 NL/L-hour, at a yield of 56%.

[0182] Operating in a positive pressure PSA mode at a cycle frequency of100 cycles/minute with feed air compressed to 3 bars absolute andexhaust at atmospheric pressure, oxygen product at 80% purity wasobtained with a specific productivity of 1320 NL/L-hour, at a yield of25.5%.

[0183] Operating in a positive pressure PSA mode at a cycle frequency of100 cycles/minute with feed air compressed to 3 bars absolute andexhaust at atmospheric pressure, oxygen product at 70% purity wasobtained with a specific productivity of 1750 NL/L-hour, at a yield of33%.

[0184] For comparison, conventional oxygen industrial vacuum-PSA and PSAsystems using granular adsorbent operate at cycle frequencies of onlyabout 1 cycle/minute, achieving specific productivities of about 30NL/L-hour. Specific productivities in the range of 130 to 170 NL/L-hourhave been reported for a prior art rotary PSA device (See Vigor et al.,U.S. Pat. No. 5,658,370). Keller et al. (U.S. Pat. No. 4,354,859)achieved specific productivities for oxygen in the range of 210 to 270NL/L-hour by operating at cycle frequencies of 45 to 50 cycles/minutewith a granular adsorber of 40 to 80 mesh zeolite.

[0185] The high specific productivities realized with the axial flowrotary PSA system of the disclosure are thus substantially better thanprior art systems, by one to two full orders of magnitude. Highproductivities from the disclosed compact PSA units are decisivelyimportant for automobile fuel cell applications, as prior art devicesare far too bulky and heavy to be considered for such applications.

[0186] It is to be noted that the extreme compactness of the PSA devicesprovided for fuel cell systems by the present invention is enabled byoperating at high cycle frequency (greater than 50 cycles per minute,and more preferably greater than 100 cycles per minute) with the dualenabling aspects of the rotary PSA mechanism and the adsorbent modulesformed of thin adsorbent sheets with narrow channels spacedtherebetween. At a specific productivity of 1500 NL/L-hour, the abovementioned PSA unit delivered about 200 NL/min of contained oxygen from amodule volume of only 16 L. This oxygen flow rate would suffice for a 40kW fuel cell, or for an even larger fuel cell if additional oxygen isprovided by blending bypass air with the PSA product oxygen.

[0187] Hydrogen Purification PSA

[0188] Hydrogen purification PSA is particularly advantageous because itsuccessfully removes impurities to a level that are not incompatiblewith PEM fuel cells. Such impurities include many compounds that areinherent to fossil fuel reforming or hydrogen recovery from chemicalplant off-gases. For example, several particularly problematiccompounds, such as ammonia, carbon monoxide, hydrogen sulfide, methanolvapor, and chlorine are removed effectively by PSA.

[0189] Methanol is a preferred feedstock for PEM fuel cells instationary and automotive applications. Steam reforming of methanolgenerates raw hydrogen or syngas containing hydrogen, carbon dioxide andsignificant levels of carbon monoxide and unreacted methanol. Thehydrogen PSA of the present disclosure has been tested on syntheticmethanol syngas containing approximately 1% carbon monoxide, methanolvapor, and water vapor along with carbon dioxide as the bulk impurity.Each of the impurities was reduced below a concentration of 50 ppm.

[0190] Autothermal reforming, steam reforming or partial oxidation ofother hydrocarbons (e.g. natural gas, gasoline, or diesel fuel)invariably produces raw hydrogen or syngas containing carbon dioxide andfrequently nitrogen as bulk impurities, with carbon monoxide andfrequently hydrogen sulfide as potentially harmful contaminants. All ofthese impurities can be adequately removed by the hydrogen PSA unit ofthe present disclosure.

[0191] The ability of the hydrogen PSA unit to remove severely harmfulcomponents such as carbon monoxide, methanol vapor and hydrogen sulfideis most important for PEM fuel cells, to extend their operating life,improve their reliability, and potentially also reduce their cost byenabling lower noble metal catalyst loadings on the fuel cellelectrodes.

[0192] The ability of the hydrogen PSA unit to remove bulk impuritiessuch as carbon dioxide and nitrogen allows the fuel cell to operate witha high partial pressure of hydrogen and with a much smaller cathodepurge flow, thus improving electrochemical energy conversion efficiencywhile also improving hydrogen utilization within the fuel cell anodechannel.

[0193] The foregoing description is intended to be illustrative of thepreferred embodiments of the present invention. Those of ordinary skillmay envisage certain additions, deletions and/or modifications to thedescribed embodiments which, although not specifically described orreferred to herein, do not depart from the spirit or scope of thepresent invention as defined by the appended claims.

We claim:
 1. An electrical current generating system comprising: a fuelcell including an anode channel including an anode gas inlet forreceiving a supply of hydrogen gas, a cathode channel including acathode gas inlet and a cathode gas outlet, and an electrolyte incommunication with the anode and cathode channel for facilitating ionexchange between the anode and cathode channel; an oxygen gas deliverysystem coupled to the cathode gas inlet for delivering a gaseous streamenriched in oxygen gas to the cathode channel, the oxygen gas deliverysystem including a rotary pressure swing adsorption system for enrichingoxygen in a gaseous feed.
 2. The system according to claim 1 and furthercomprising a first gas recirculation means coupled to the cathode gasoutlet for recirculating a first portion of cathode exhaust gasexhausted from the cathode channel to the cathode gas inlet.
 3. Thecurrent generating system according to claim 1 where the pressure swingadsorption system includes a first feed gas inlet for receiving air feedas a first gas feed, and a gas outlet coupled to the cathode gas inlet.4. The current generating system according to claim 3 where the oxygengas delivery system includes a gas inlet for receiving a first portionof cathode gas exhausted from the cathode channel and a gas outlet fordelivering the gaseous stream enrich in oxygen gas to the cathodechannel.
 5. The current generating system according to claim 4 where theoxygen gas delivery system includes a first gas recirculation meanscoupled to the cathode gas outlet for recirculating the first portion ofcathode gas from the cathode channel to the cathode gas inlet.
 6. Thecurrent generating system according to claim 5, wherein the first gasrecirculating means comprises a compressor for supplying the firstcathode exhaust gas portion under pressure to the cathode gas inlet. 7.The current generating system according to claim 6, wherein the firstgas recirculation means includes a condensate separator coupled betweenthe cathode gas outlet and the compressor for removing moisture from thefirst cathode exhaust gas portion.
 8. The current generating systemaccording to claim 6, wherein the FIRST gas recirculating means directsthe first cathode exhaust gas portion as feed gas to the gas separationsystem.
 9. The current generating system according to claim 4, whereinthe gas separation system includes a second feed gas inlet, and thecurrent generating system includes second gas recirculating meanscoupled to the cathode gas outlet for recirculating a second portion ofthe cathode exhaust gas to the second feed gas inlet.
 10. The currentgenerating system according to claim 9 wherein the recirculating meanscomprises a restrictive orifice for delivering the second cathodeexhaust gas portion to the gas separation system at a pressure less thana pressure of the air feed.
 11. The current generating system accordingto claim 9 where the pressure swing adsorption system comprises a rotarymodule including a stator and a rotor rotatable relative to the stator,the rotor including a plurality of flow paths for receiving adsorbentmaterial therein for preferentially adsorbing a first gas component inresponse to increasing pressure in the flow paths relative to a secondgas component, and compression machinery coupled to the rotary modulefor facilitating gas flow through the flow paths for separating thefirst gas component from the second gas component.
 12. The currentgenerating system according to claim 11 wherein the plurality of flowpaths are aligned with the axis of the rotor.
 13. The current generatingsystem according to claim 11, wherein the stator includes a first statorvalve surface, a second stator valve surface, a plurality of firstfunction compartments opening into the first stator valve surface, and aplurality of second function compartments opening into the second statorvalve surface, and the rotor includes a first rotor valve surface incommunication with the second stator valve surface, and a plurality ofapertures provided in the rotor valve surfaces and in communication withrespective ends of the flow paths and the function compartments.
 14. Thecurrent generating system according to claim 13 where the compressionmachinery is coupled to a portion of the function compartments formaintaining the portion of function compartments at a plurality ofdiscrete respective pressure levels between an upper pressure and alower pressure for maintaining uniform gas flow through the portion offunction compartments.
 15. The current generating system according toclaim 13, wherein the function compartments include a light reflux exitcompartment and a light reflux return compartment, the compressionmachinery comprises a light reflux expander coupled between the lightreflux exit and return compartments, and the first gas recirculationmeans comprises a compressor coupled to the light reflux expander forsupplying the first cathode exhaust gas portion under pressure to thecathode gas inlet
 16. The current generating system according to claim15 wherein the rotary pressure swing adsorption system includes a heaterdisposed between the light reflux exit compartment and the light refluxexpander for enhancing recovery of energy from light reflux gasexhausted from the light reflux exit compartment.
 17. The currentgenerating system according to claim 15 where the function compartmentsinclude a gas feed compartment and a countercurrent blowdowncompartment, and the compression machinery comprises a compressorcoupled to the first feed gas inlet for delivering compressed air to thegas feed compartment, and an expander coupled to the compressor forexhausting heavy product gas enriched in the first gas component fromthe countercurrent blowdown compartment.
 18. The current generatingsystem according to claim 15 where the function compartments include acountercurrent blowdown compartment and a heavy product compartment, andthe compression machinery comprises an expander coupled to thecountercurrent blowdown compartment.
 19. The current generating systemaccording to claim 18 further comprising a vacuum pump coupled to theexpander for extracting heavy product gas enriched in the first gascomponent at subatmospheric pressure from the heavy product compartment.20. The current generating system according to claim 13 where thefunction compartments include a gas feed compartment, and the gasrecirculating means directs the first cathode exhaust gas portion asfeed gas to the gas feed compartment.
 21. The current generating systemaccording to claim 13 where the function compartments include a gas feedcompartment, and the current generating system includes second gasrecirculating means coupled to the cathode gas outlet for recirculatinga second portion of the cathode exhaust gas to the gas feed compartment.22. The current generating system according to claim 21 where the secondgas recirculating means comprises a restrictor orifice.
 23. The currentgenerating system according to claim 11 where the adsorbent material isone of CA-X, Li—X, lithium chabazite zeolite, calcium-exchangedchabazite and strontium-exchanged chabazite.
 24. The current generationsystem according to claim 1 where the rotary pressure swing adsorptionsystem enriches oxygen and removes carbon dioxide from an air feed. 25.The current generation system according to claim 24 further comprising ahydrogen gas delivery system coupled to the anode gas inlet.
 26. Thecurrent generation system according to claim 25 where the hydrogen gasdelivery system enriches hydrogen gas in a gaseous feed.
 27. The currentgeneration system according to claim 26 further comprising an oxygenaccumulator interposed between the oxygen gas delivery system and thecathode gas inlet
 28. The current generation system according to claim27 in which the electrolyte is alkaline and is maintained at a workingtemperature greater that about 100° C., the oxygen gas delivery systemis operated to supply oxygen of about 90% purity to the cathode gasinlet, so that the product water of the fuel cell is delivered asconcentrated dry steam from the cathode gas outlet; the system includinga steam expander to expand the steam from the cathode gas outlet to avacuum condenser, a condensate pump to exhaust liquid from thecondenser, and a vacuum pump cooperating with the oxygen pressure swingadsorption system and exhausting permanent gas overheads from the vacuumcondenser.
 29. Electrical current generated by the electrical currentgenerating system according to claim
 1. 30. The current generatingsystem according to claim 8 where the rotary pressure swing adsorptionsystem comprises a rotary module for implementing a pressure swingadsorption process having an operating pressure cycling between an upperpressure and a lower pressure, for extracting a first gas fraction and asecond gas fraction from a gas mixture including the first and secondfractions, the rotary module comprising: a stator including a firststator valve surface, a second stator valve surface a plurality of firstfunction compartments opening into the first stator valve surface, and aplurality of second function compartments opening into the second statorvalve surface; and a rotor rotatably coupled to the stator and includinga first rotor valve surface in communication with the first stator valvesurface, a second rotor valve surface in communication with the secondstator valve surface, a plurality of flow paths for receiving adsorbentmaterial therein, each said flow path including a pair of opposite ends,and a plurality of apertures provided in the rotor valve surfaces and incommunication with the flow path ends and the functions ports forcyclically exposing each said flow path to a plurality of discretepressure levels between the upper and lower pressure for maintaininguniform gas floe through the first and second function compartments, thefunction compartments comprising first and second gas geed compartmentsopening into the firs stator valve surface for delivering the gasmixture to the flow paths for sequentially exposing the flow paths tothe second feed gas prior to the firs feed gas.
 31. The currentgeneration system according to claim 30 where the second feed gas isenriched in oxygen relative to the first feed gas.
 32. An electricalcurrent generating system comprising: a fuel cell including an anodechannel including an anode gas inlet and an anode gas outlet, a cathodechannel including a cathode gas inlet and a cathode gas outlet, and anelectrolyte in communication with the anode and cathode channel forfacilitating exchange between the anode and cathode channel; an oxygengas delivery system coupled to the cathode gas inlet for deliveringoxygen gas to the cathode channel; and a hydrogen gas delivery systemcoupled to the anode gas inlet for delivering a gaseous stream enrichedin hydrogen gas to the anode channel, including a first rotary pressureswing adsorption system for enriching hydrogen in a gaseous feed
 33. Theelectrical current generation system according to claim 32 where thefirst rotary pressure sing adsorption system includes a first gas feedgas inlet for receiving a first gas feed comprising hydrogen gas and agas outlet coupled to the anode gas inlet.
 34. The electrical currentgeneration system according to claim 33 where the hydrogen gas deliverysystem includes a gas inlet for receiving a second gas feed from theanode gas outlet and a gas outlet for delivering the gaseous streamenriched in hydrogen gas to the anode channel.
 35. The electricalcurrent generation system according to claim 34 where the second gasfeed is passed through the first rotary pressure swing adsorptionsystem.
 36. The electrical current generation system according to claim35 where the first rotary pressure swing adsorption system includes asecond feed gas inlet for receiving the second gas feed.
 37. Theelectrical current generating system according to claim 32 where theoxygen gas delivery system comprises an oxygen gas separation system forextracting oxygen gas from air, the gas separation system including afirst feed gas inlet for receiving an air feed, and an oxygen gas outletcoupled to the cathode gas inlet for supplying enriched oxygen gas tothe cathode channel from the air feed.
 38. The electrical currentgeneration system according to claim 36 where the oxygen gas deliverysystem comprises a second rotary pressure swing adsorption system forextracting oxygen gas from the air, the second rotary pressure swingadsorption system including a first feed gas inlet for receiving an airfeed an a gas outlet coupled to the cathode gas inlet for supplying agaseous stream enriched in oxygen gas to the cathode channel.
 39. Theelectrical current generating system according to claim 36 where thehydrogen gas delivery system comprises a reactor for producing a secondgas feed from hydrocarbon fuel, and wherein the first rotary pressureswing adsorption system is coupled to the reactor for receiving thefirst and second gas feeds.
 40. The electrical current generating systemaccording to claim 39 wherein the hydrogen gas delivery system comprisesa reactor for producing a second hydrogen gas feed from hydrocarbonfuel, and wherein the first rotary pressure swing adsorption system iscoupled to the reactor and receives the first and second gas feeds. 41.The electrical current generating system according to claim 40 where thefirst rotary pressure swing adsorption system receives the first andsecond gas feeds, and produces a gaseous stream enriched in hydrogentherefrom.
 42. The electrical current generating system according toclaim 41 where the first rotary pressure swing adsorption systemhydrogen includes a first feed gas inlet for receiving the first gasfeed, and a second feed gas inlet for receiving the second gas feed. 43.The electrical current generating system according to claim 42 where thefirst gas feed is provided at a pressure level different from a pressurelevel of the second gas feed.
 44. The electrical current generatingsystem according to claim 43 where the reactor comprises a steamreformer, and a water gas shift reactor coupled to the steam reformerfor producing the second gas feed.
 45. The electrical current generatingsystem according to claim 44 where the steam reformer includes a burnerincluding a first burner inlet coupled to the cathode gas outlet forreceiving humid oxygen-enriched gas, and a second burner inlet forreceiving heavy product from the first rotary pressure swing adsorptionsystem for burning within the burner for providing endothermic heat ofreaction for steam reforming the hydrocarbon fuel.
 46. The electricalcurrent generating system according to claim 39 wherein the reactorcomprises an autothermal reformer, and a water gas shift reactor coupledto the steam reformer for producing the second gas feed.
 47. Theelectrical current generating system according to claim 46 where theoxygen gas delivery system comprises a second rotary pressure swingadsorption system for extracting oxygen gas from air, the second rotarypressure swing adsorption system including a first feed gas inlet forreceiving an air feed, and a gas outlet coupled to the cathode gas inletfor supplying a gaseous stream enriched in oxygen gas to the cathodechannel, and the reactor comprises a burner including a first burnerinlet for receiving air, and a second burner inlet for receiving agaseous stream enriched in hydrogen gas from the first rotary pressureswing adsorption system for burning the received hydrogen gas within theburner for recovery of heat energy for pressurizing the air feed. 48.The electrical current generating system according to claim 47 where atleast one of the pressure swing adsorption systems comprises a rotarymodule including a stator and a rotor rotatable relative to the stator,the rotor including a plurality of flow paths for receiving adsorbentmaterial therein for preferentially adsorbing a first gas component inresponse to increasing pressure in the flow paths relative to a secondgas component, and compression machinery coupled to the rotary modulefor facilitating gas flow through the flow paths for separating thefirst gas component from the second gas component.
 49. The currentgenerating system according to claim 48 where the stator includes afirst stator valve surface, a second stator valve surface, a pluralityof first function compartments opening into the first stator valvesurface, and the rotor includes a first rotor valve surface incommunication with the first stator valve surface, a second rotor valvesurface in communication with the second stator valve surface, and aplurality of apertures provided in the rotor valve surfaces and incommunication with respective ends of the flow paths and the functioncompartments.
 50. The current generating system according to claim 49wherein the compression machinery is coupled to a portion of thefunction compartments for maintaining the portion of functioncompartments at a plurality of discrete respective pressure levelsbetween an upper pressure and a lower pressure for maintaining uniformgas flow through the portion of function compartments.
 51. Theelectrical generating system according to claim 33 further comprising agas recirculation means coupled to the cathode gas outlet forrecirculating a portion of cathode exhaust gas exhausted from thecathode channel to the cathode gas inlet.
 52. The electrical generatingsystem according to claim 39 further comprising a gas recirculationmeans coupled to the cathode gas outlet for recirculating a portion ofcathode exhaust gas exhausted from the cathode channel to the reactorfor producing hydrogen from hydrocarbon fuel.
 53. Electrical currentgenerated by the electrical current generating system of claim
 33. 54. Amethod of generating an electric potential, comprising: providing a fuelcell including an anode channel including an anode gas inlet, a cathodechannel including a cathode gas inlet and a cathode gas outlet, and anelectrolyte in communication with the anode and cathode channel forfacilitating ion exchange between the anode and cathode channel;supplying a gaseous stream enriched in oxygen gas to the cathode gasinlet, where the supplying step comprises supplying a first gas feed toa rotary pressure swing adsorption apparatus to produce a product gasstream enriched in oxygen gas; and delivering the product gas stream tothe cathode gas inlet.
 55. The method according to claim 54 and furthercomprising recirculating a portion of cathode gas exhausted from thecathode gas outlet to the cathode gas inlet.
 56. The method according toclaim 55 where recirculating comprises delivering the exhaust gasportion to the rotary pressure swing adsorption apparatus as a secondgas geed.
 57. The method according to claim 56 where the recirculatingfurther comprises purging a remainder of the exhausted cathode gas. 58.The method according to claim 57 where recirculating comprisesdelivering the exhaust gas portion at increased pressure to the cathodegas inlet.
 59. The method according to claim 58 where recirculatingfurther comprises recovering waste heat from the fuel cell for enhancingrecovery of expansion energy from the pressure swing adsorptionapparatus.
 60. The method according to claim 54 where supplying hydrogengas comprises recirculating a portion of cathode gas exhausted from thecathode gas outlet to the inlet of a fuel processor for reacting ahydrocarbon fuel to generate hydrogen.
 61. A method for generatingelectrical potential, comprising: providing a fuel cell including ananode channel including an anode gas inlet, a cathode channel includinga cathode gas inlet and a cathode gas outlet, and an electrolyte incommunication with the anode and cathode channel for facilitating tonexchange between the anode and cathode channel; supplying a firstgaseous stream enriched in hydrogen gas to the anode gas inlet, wheresupplying comprises supplying a first gas feed to a rotary hydrogenpressure swing adsorption apparatus to produce a first product gasstream enriched in hydrogen gas; delivering the first product gas streamto the anode gas inlet; and supplying a second gaseous stream enrichedin oxygen gas to the cathode gas inlet.
 62. The method according toclaim 61 and further comprising recirculating a portion of anode gasexhausted from the anode gas outlet to the anode gas inlet.
 63. Themethod according to claim 62 where recirculating comprises deliveringthe exhaust gas portion to the rotary hydrogen pressure swing adsorptionapparatus as a second gas feed.
 64. The method according to claim 63where supplying a second gaseous stream comprises supplying an air feedto a rotary oxygen pressure swing adsorption apparatus to produce asecond product gas stream enriched in oxygen gas, and delivering thesecond product gas stream to the cathode gas inlet.
 65. The methodaccording to claim 64where supplying hydrogen gas comprises supplying ahydrocarbon fuel to a reformer, reacting the fuel with oxygen-enrichedgas from the cathode gas outlet, delivering a hydrogen gas feed from thereformer as a first gas feed to a hydrogen pressure swing adsorptionapparatus, and delivering hydrogen-enriched gas extracted from the firstgas feed as light product gas to the anode gas inlet.
 66. The methodaccording to claim 65 where the reformer comprises a steam reformerincluding a combustor, and reacting comprises delivering the fuel to thecombustor, and providing heat energy to the combustor by burning tailgas extracted from the rotary hydrogen pressure swing adsorptionapparatus as heavy product gas with the oxygen-enriched gas from thecathode gas outlet in the combustor.
 67. The method according to claim65 where the reformer comprises a steam reformer including a combustor,and reacting comprises delivering the fuel to the combustor, andproviding heat energy to the combustor by burning tail gas extractedfrom the rotary hydrogen pressure swing adsorption apparatus as heavyproduct gas with a portion of the air feed in the combustor, andrecovering heat of combustion from the combustor for delivering airunder pressure to the rotary oxygen pressure swing adsorption apparatus.68. The method according to claim 65 where the reformer comprises anautothermal reformer including a water gas shift reactor, and the stepof supplying a pressurized air feed comprises the steps of deliveringair to a combustor, burning tail gas extracted from the hydrogenpressure swing adsorption apparatus as heavy product gas with thedelivered air in the combustor, and recovering heat of combustion fromthe combustor for delivering air under pressure to the oxygen pressureswing adsorption apparatus.
 69. An electrical current generating systemcomprising: a fuel cell including an anode channel including an anodegas inlet and an anode gas outlet, a cathode channel including a cathodegas inlet and a cathode gas outlet, and an electrolyte in communicationwith the anode and cathode channel for facilitating ion exchange betweenthe anode and cathode channel; an oxygen gas delivery system coupled tothe cathode gas inlet for delivering enriched oxygen gas to the cathodechannel, the oxygen gas delivery system including a pressure swingadsorption system to enrich oxygen and to remove carbon dioxide fromatmospheric air feed; and a hydrogen gas delivery system coupled to theanode gas inlet for delivering purified hydrogen gas to the cathodechannel.
 70. The current generating system according to claim 69 furtherincluding an oxygen accumulator interposed between the oxygen gasdelivery system and the cathode gas inlet. The method according to claim65 where the reformer comprises a steam reformer including a combustor,and reacting comprises delivering the fuel to the combustor, andproviding heat energy to the combustor by burning tail gas extractedfrom the hydrogen pressure swing adsorption apparatus as heavy productgas with the oxygen-enriched gas from the cathode gas outlet in thecombustor.
 71. The electrical current generation system according toclaim 1 where the rotary pressure swing adsorption system comprises aplurality of adsorbers having first and second ends communicatingrespectively to a first valve face and a second valve face, theplurality of adsorbers being housed in an adsorber housing bodycooperating with first and second valve bodies respectively sealinglyengaged with the adsorber housing body at the first and second valvefaces.
 72. The electrical current generation system according to claim71 where the adsorber housing body rotates relative to the first andsecond valve bodies.
 73. The electrical current generation systemaccording to claim 71 where the first and second valve bodies rotaterelative to the adsorber housing.
 74. The electrical current generationsystem according to claim 73 where the rotary pressure swing adsorptionsystem further comprises transfer chambers providing fluid communicationbetween the first valve body and respectively a feed air inlet conduitand an exhaust discharge conduit.
 75. The electrical current generationsystem according to claim 73 where the rotary pressure swing adsorptionsystem further comprises a transfer chamber providing fluidcommunication between the second valve body and the product oxygenconduit to the cathode inlet.
 76. The electrical current generationsystem according to claim 1 further where the pressure swing adsorptionsystem generates a gaseous stream enriched in oxygen, the gaseous streamenriched in oxygen having a first oxygen purity and being fluidlycoupled to the cathode gas inlet, the system further comprising acompressed air inlet for mixing compressed air with the gaseous streamenriched in oxygen upstream of the cathode gas inlet, thereby forming acathode feed gas stream having a second oxygen purity lower than thefirst oxygen purity.
 77. The electrical current generation system wherethe first oxygen purity is in the range of from about 70% to about 90%and the second oxygen purity is in the range of from about 30% to about40%.